Virtuoso 7.2.12 crashes at `dc_append_bytes`. It can also be reproduced on the latest commit 2bbd7e0.

PoC:
```sql
SELECT 1 FROM (SELECT 1 x) AS x GROUP BY REPEAT(REPEAT('1', 70), 100000)
```

GDB backtrace (on commit 2bbd7e0):
```
Thread 8 "virtuoso-t" received signal SIGSEGV, Segmentation fault.
[Switching to LWP 1162395]
0x00007fa3cf590a84 in ?? () from target:/lib/x86_64-linux-gnu/libc.so.6
(gdb) bt
#0  0x00007fa3cf590a84 in ?? () from target:/lib/x86_64-linux-gnu/libc.so.6
#1  0x000055f6b6f886e9 in memcpy_16 (t=0x7fa3b4e77008, s=0x7fa3b7a67658, len=7000005) at Dkmem.c:91
#2  0x000055f6b6b79ed5 in dc_append_bytes (dc=0x7fa3b6c65090, bytes=0x7fa3b7a67658 "\266", len=7000005, pref_bytes=0x0, pref_len=0) at vec.c:356
#3  0x000055f6b68531a1 in dc_append_cha (dc=0x7fa3b6c65090, ha=0x7fa3a000f750, cha=0x7fa3b7939088, row=0x7fa3b7adf658, col=0) at chash.c:2654
#4  0x000055f6b6853ebb in chash_read_input (ts=0x7fa3a001f7e0, inst=0x7fa3a0020a08, state=0x7fa3a0020a08) at chash.c:2843
#5  0x000055f6b6ae8bbf in qn_input (xx=0x7fa3a001f7e0, inst=0x7fa3a0020a08, state=0x7fa3a0020a08) at sqlrun.c:982
#6  0x000055f6b6ae8e72 in qn_send_output (src=0x7fa3a001e0e0, state=0x7fa3a0020a08) at sqlrun.c:1028
#7  0x000055f6b6af3112 in fun_ref_node_input (fref=0x7fa3a001e0e0, inst=0x7fa3a0020a08, state=0x7fa3a0020a08) at sqlrun.c:3547
#8  0x000055f6b6ae8bbf in qn_input (xx=0x7fa3a001e0e0, inst=0x7fa3a0020a08, state=0x7fa3a0020a08) at sqlrun.c:982
#9  0x000055f6b6ae8e72 in qn_send_output (src=0x7fa3a001dfd0, state=0x7fa3a0020a08) at sqlrun.c:1028
#10 0x000055f6b6b3dbf4 in set_ctr_vec_input (sctr=0x7fa3a001dfd0, inst=0x7fa3a0020a08, state=0x7fa3a0020a08) at sqlvnode.c:642
#11 0x000055f6b69ce698 in set_ctr_input (sctr=0x7fa3a001dfd0, inst=0x7fa3a0020a08, state=0x7fa3a0020a08) at sort.c:1317
#12 0x000055f6b6ae8bbf in qn_input (xx=0x7fa3a001dfd0, inst=0x7fa3a0020a08, state=0x7fa3a0020a08) at sqlrun.c:982
#13 0x000055f6b6af5f04 in qr_exec (cli=0x7fa3a0000e30, qr=0x7fa3a001a360, caller=0x2, cr_name=0x7fa3a0021608 "s1111_1_0", stmt=0x7fa3a0018b10, lc_ret=0x0, parms=0x7fa3ac022668, opts=0x55f6bbe64728, named_params=0) at sqlrun.c:4343
#14 0x000055f6b6b00575 in sf_sql_execute (stmt_id=0x7fa3ac022688 "s1111_1_0", text=0x55f6bbe67358 "\320\b", cursor_name=0x7fa3ac022728 "s1111_1_0", params=0x7fa3ac022708, current_ofs=0x7fa3ac022648, options=0x55f6bbe64728) at sqlsrv.c:2008
#15 0x000055f6b6b009bd in sf_sql_execute_w (stmt_id=0x7fa3ac022688 "s1111_1_0", text=0x55f6bbe67358 "\320\b", cursor_name=0x7fa3ac022728 "s1111_1_0", params=0x7fa3ac022708, current_ofs=0x7fa3ac022648, options=0x55f6bbe64728) at sqlsrv.c:2051
#16 0x000055f6b6b07502 in sf_sql_execute_wrapper (args=0x7fa3b64d8c50) at sqlsrv.c:3997
#17 0x000055f6b6f9ba18 in future_wrapper (ignore=0x0) at Dkernel.c:1171
#18 0x000055f6b6fa8515 in _thread_boot (arg=0x7fa3ac011bb0) at sched_pthread.c:296
#19 0x00007fa3cf756609 in start_thread () from target:/lib/x86_64-linux-gnu/libpthread.so.0
#20 0x00007fa3cf524353 in clone () from target:/lib/x86_64-linux-gnu/libc.so.6
```
Virtuoso 7.2.12 crashes at `dc_append_bytes`
This is a GitHub Issue
repo:virtuoso-opensource
owner:openlink
Title : Virtuoso 7.2.12 crashes at `dc_append_bytes`
Issue date:

--- start body ---
Virtuoso 7.2.12 crashes at `dc_append_bytes`. It can also be reproduced on the latest commit 2bbd7e0.

PoC:
```sql
SELECT 1 FROM (SELECT 1 x) AS x GROUP BY REPEAT(REPEAT('1', 70), 100000)
```

GDB backtrace (on commit 2bbd7e0):
```
Thread 8 "virtuoso-t" received signal SIGSEGV, Segmentation fault.
[Switching to LWP 1162395]
0x00007fa3cf590a84 in ?? () from target:/lib/x86_64-linux-gnu/libc.so.6
(gdb) bt
#0  0x00007fa3cf590a84 in ?? () from target:/lib/x86_64-linux-gnu/libc.so.6
#1  0x000055f6b6f886e9 in memcpy_16 (t=0x7fa3b4e77008, s=0x7fa3b7a67658, len=7000005) at Dkmem.c:91
#2  0x000055f6b6b79ed5 in dc_append_bytes (dc=0x7fa3b6c65090, bytes=0x7fa3b7a67658 "\266", len=7000005, pref_bytes=0x0, pref_len=0) at vec.c:356
#3  0x000055f6b68531a1 in dc_append_cha (dc=0x7fa3b6c65090, ha=0x7fa3a000f750, cha=0x7fa3b7939088, row=0x7fa3b7adf658, col=0) at chash.c:2654
#4  0x000055f6b6853ebb in chash_read_input (ts=0x7fa3a001f7e0, inst=0x7fa3a0020a08, state=0x7fa3a0020a08) at chash.c:2843
#5  0x000055f6b6ae8bbf in qn_input (xx=0x7fa3a001f7e0, inst=0x7fa3a0020a08, state=0x7fa3a0020a08) at sqlrun.c:982
#6  0x000055f6b6ae8e72 in qn_send_output (src=0x7fa3a001e0e0, state=0x7fa3a0020a08) at sqlrun.c:1028
#7  0x000055f6b6af3112 in fun_ref_node_input (fref=0x7fa3a001e0e0, inst=0x7fa3a0020a08, state=0x7fa3a0020a08) at sqlrun.c:3547
#8  0x000055f6b6ae8bbf in qn_input (xx=0x7fa3a001e0e0, inst=0x7fa3a0020a08, state=0x7fa3a0020a08) at sqlrun.c:982
#9  0x000055f6b6ae8e72 in qn_send_output (src=0x7fa3a001dfd0, state=0x7fa3a0020a08) at sqlrun.c:1028
#10 0x000055f6b6b3dbf4 in set_ctr_vec_input (sctr=0x7fa3a001dfd0, inst=0x7fa3a0020a08, state=0x7fa3a0020a08) at sqlvnode.c:642
#11 0x000055f6b69ce698 in set_ctr_input (sctr=0x7fa3a001dfd0, inst=0x7fa3a0020a08, state=0x7fa3a0020a08) at sort.c:1317
#12 0x000055f6b6ae8bbf in qn_input (xx=0x7fa3a001dfd0, inst=0x7fa3a0020a08, state=0x7fa3a0020a08) at sqlrun.c:982
#13 0x000055f6b6af5f04 in qr_exec (cli=0x7fa3a0000e30, qr=0x7fa3a001a360, caller=0x2, cr_name=0x7fa3a0021608 "s1111_1_0", stmt=0x7fa3a0018b10, lc_ret=0x0, parms=0x7fa3ac022668, opts=0x55f6bbe64728, named_params=0) at sqlrun.c:4343
#14 0x000055f6b6b00575 in sf_sql_execute (stmt_id=0x7fa3ac022688 "s1111_1_0", text=0x55f6bbe67358 "\320\b", cursor_name=0x7fa3ac022728 "s1111_1_0", params=0x7fa3ac022708, current_ofs=0x7fa3ac022648, options=0x55f6bbe64728) at sqlsrv.c:2008
#15 0x000055f6b6b009bd in sf_sql_execute_w (stmt_id=0x7fa3ac022688 "s1111_1_0", text=0x55f6bbe67358 "\320\b", cursor_name=0x7fa3ac022728 "s1111_1_0", params=0x7fa3ac022708, current_ofs=0x7fa3ac022648, options=0x55f6bbe64728) at sqlsrv.c:2051
#16 0x000055f6b6b07502 in sf_sql_execute_wrapper (args=0x7fa3b64d8c50) at sqlsrv.c:3997
#17 0x000055f6b6f9ba18 in future_wrapper (ignore=0x0) at Dkernel.c:1171
#18 0x000055f6b6fa8515 in _thread_boot (arg=0x7fa3ac011bb0) at sched_pthread.c:296
#19 0x00007fa3cf756609 in start_thread () from target:/lib/x86_64-linux-gnu/libpthread.so.0
#20 0x00007fa3cf524353 in clone () from target:/lib/x86_64-linux-gnu/libc.so.6
```
--- end body ---
