An issue in the list_append component of MonetDB Server v11.45.17 and v11.46.0 allows attackers to cause a Denial of Service (DoS) via crafted SQL statements.
**Describe the bug**
MonetDB server 11.46.0 crashes at `list_append` after executing SQL statements through mclient.

**To Reproduce**
```sql
create table t1(c1 int auto_increment primary key NOT NULL);
create trigger i1 after insert on t1 for each row insert into t1 values(NULL);
insert into t1 values(NULL);
```

**Expected behavior**
This crash is strange. From the backtrace as follows, we can know that the crash is caused by infinite recursion.

However, if we change the first statement into `create table t1(c1 int);`, the MonetDB will return the message `Query too complex: running out of stack space` when executing the third stmt. So, MonetDB handles out of stack space, but it does not work with some special table definitions?

What's more, the definition of the table contains the `NOT NULL` constraint, which should fail the third stmt. If we remove the create trigger statement, MonetDB will return the message `INSERT INTO: NOT NULL constraint violated for column t1.c1` when executing the insert stmt. But with the create trigger stmt, it crashes instead.

Anyway, I think the expected behavior is to return the error message `Query too complex: running out of stack space`  or `INSERT INTO: NOT NULL constraint violated for column t1.c1`, instead of crashing straightly.

**Backtrace**
```
#0 0x7f0c3760dbda (list_append+0x1a)
#1 0x7f0c376669c6 (rel_insert+0x196)
#2 0x7f0c3766abb3 (rel_updates+0x1ce3)
#3 0x7f0c376c6c11 (sequential_block+0x121)
#4 0x7f0c376c52dc (rel_psm+0x131c)
#5 0x7f0c37653091 (rel_semantic+0x91)
#6 0x7f0c37652e6a (rel_parse+0x19a)
#7 0x7f0c37563102 (sql_insert_triggers+0x232)
#8 0x7f0c3755bb5e (rel2bin_insert+0x148e)
#9 0x7f0c37554539 (subrel_bin+0xd69)
#10 0x7f0c3755f218 (exp_bin+0x29e8)
#11 0x7f0c37558567 (subrel_bin+0x4d97)
#12 0x7f0c37563162 (sql_insert_triggers+0x292)
#13 0x7f0c3755bb5e (rel2bin_insert+0x148e)
#14 0x7f0c37554539 (subrel_bin+0xd69)
#15 0x7f0c3755f218 (exp_bin+0x29e8)
#16 0x7f0c37558567 (subrel_bin+0x4d97)
#17 0x7f0c37563162 (sql_insert_triggers+0x292)
...
#7407 0x7f0c37563162 (sql_insert_triggers+0x292)
#7408 0x7f0c3755bb5e (rel2bin_insert+0x148e)
#7409 0x7f0c37554539 (subrel_bin+0xd69)
#7410 0x7f0c3755373b (output_rel_bin+0x6b)
#7411 0x7f0c3757f9d9 (backend_dumpstmt+0x199)
#7412 0x7f0c3754a367 (SQLparser+0x5d7)
#7413 0x7f0c3754987b (SQLengine_+0x59b)
#7414 0x7f0c37548343 (SQLengine+0x23)
#7415 0x7f0c378d76cf (runScenario+0x4f)
#7416 0x7f0c378d816c (MSscheduleClient+0x68c)
#7417 0x7f0c3797fc2b (doChallenge+0xfb)
#7418 0x7f0c37ffeba0 (THRstarter+0x100)
#7419 0x7f0c3806ecc4 (thread_starter+0x34)
#7420 0x7f0c373e3609 (start_thread+0xd9)
#7421 0x7f0c37308133 (clone+0x43)
```

**Software versions**
 - MonetDB server version: 11.46.0 (hg id: 63a42c2) (pulled from the master branch)
 - MonetDB client version: mclient, version 11.48.0 (hg id: 63a42c2)
 - OS and version: ubuntu 20.04
 - Self-installed and compiled. The command line of compilation: `CC=clang-12 CXX=clang++-12 cmake /root/monetdb_master -DCMAKE_BUILD_TYPE=RelWithDebInfo`

**Issue labeling**
bug

**Additional context**
The MonetDB here runs in-memory database. The command line of starting MonetDB server is `mserver5 --in-memory`.
MonetDB server 11.46.0 crashes at `list_append`
This is a GitHub Issue
repo:MonetDB
owner:MonetDB
Title : MonetDB server 11.46.0 crashes at `list_append`
Issue date:

--- start body ---
**Describe the bug**
MonetDB server 11.46.0 crashes at `list_append` after executing SQL statements through mclient.

**To Reproduce**
```sql
create table t1(c1 int auto_increment primary key NOT NULL);
create trigger i1 after insert on t1 for each row insert into t1 values(NULL);
insert into t1 values(NULL);
```

**Expected behavior**
This crash is strange. From the backtrace as follows, we can know that the crash is caused by infinite recursion.

However, if we change the first statement into `create table t1(c1 int);`, the MonetDB will return the message `Query too complex: running out of stack space` when executing the third stmt. So, MonetDB handles out of stack space, but it does not work with some special table definitions?

What's more, the definition of the table contains the `NOT NULL` constraint, which should fail the third stmt. If we remove the create trigger statement, MonetDB will return the message `INSERT INTO: NOT NULL constraint violated for column t1.c1` when executing the insert stmt. But with the create trigger stmt, it crashes instead.

Anyway, I think the expected behavior is to return the error message `Query too complex: running out of stack space`  or `INSERT INTO: NOT NULL constraint violated for column t1.c1`, instead of crashing straightly.

**Backtrace**
```
#0 0x7f0c3760dbda (list_append+0x1a)
#1 0x7f0c376669c6 (rel_insert+0x196)
#2 0x7f0c3766abb3 (rel_updates+0x1ce3)
#3 0x7f0c376c6c11 (sequential_block+0x121)
#4 0x7f0c376c52dc (rel_psm+0x131c)
#5 0x7f0c37653091 (rel_semantic+0x91)
#6 0x7f0c37652e6a (rel_parse+0x19a)
#7 0x7f0c37563102 (sql_insert_triggers+0x232)
#8 0x7f0c3755bb5e (rel2bin_insert+0x148e)
#9 0x7f0c37554539 (subrel_bin+0xd69)
#10 0x7f0c3755f218 (exp_bin+0x29e8)
#11 0x7f0c37558567 (subrel_bin+0x4d97)
#12 0x7f0c37563162 (sql_insert_triggers+0x292)
#13 0x7f0c3755bb5e (rel2bin_insert+0x148e)
#14 0x7f0c37554539 (subrel_bin+0xd69)
#15 0x7f0c3755f218 (exp_bin+0x29e8)
#16 0x7f0c37558567 (subrel_bin+0x4d97)
#17 0x7f0c37563162 (sql_insert_triggers+0x292)
...
#7407 0x7f0c37563162 (sql_insert_triggers+0x292)
#7408 0x7f0c3755bb5e (rel2bin_insert+0x148e)
#7409 0x7f0c37554539 (subrel_bin+0xd69)
#7410 0x7f0c3755373b (output_rel_bin+0x6b)
#7411 0x7f0c3757f9d9 (backend_dumpstmt+0x199)
#7412 0x7f0c3754a367 (SQLparser+0x5d7)
#7413 0x7f0c3754987b (SQLengine_+0x59b)
#7414 0x7f0c37548343 (SQLengine+0x23)
#7415 0x7f0c378d76cf (runScenario+0x4f)
#7416 0x7f0c378d816c (MSscheduleClient+0x68c)
#7417 0x7f0c3797fc2b (doChallenge+0xfb)
#7418 0x7f0c37ffeba0 (THRstarter+0x100)
#7419 0x7f0c3806ecc4 (thread_starter+0x34)
#7420 0x7f0c373e3609 (start_thread+0xd9)
#7421 0x7f0c37308133 (clone+0x43)
```

**Software versions**
 - MonetDB server version: 11.46.0 (hg id: 63a42c2) (pulled from the master branch)
 - MonetDB client version: mclient, version 11.48.0 (hg id: 63a42c2)
 - OS and version: ubuntu 20.04
 - Self-installed and compiled. The command line of compilation: `CC=clang-12 CXX=clang++-12 cmake /root/monetdb_master -DCMAKE_BUILD_TYPE=RelWithDebInfo`

**Issue labeling**
bug

**Additional context**
The MonetDB here runs in-memory database. The command line of starting MonetDB server is `mserver5 --in-memory`.
--- end body ---
