Virtuoso 7.2.12 crashes at `virtpcre_exec`.

PoC:
```sql
SELECT REGEXP_REPLACE('a', 'a', 'a', 9999999999999999999.9999999999999999999e-1, 0, NULL);
```

Backtrace:
```
#0 0xf20edd (virtpcre_exec+0x11ad)
#1 0xc594d0 (bif_regexp_parse_impl+0x430)
#2 0x755674 (ins_call_bif+0xc4)
#3 0x763539 (code_vec_run_1+0xdf9)
#4 0x7b9841 (qn_input+0x3c1)
#5 0x7cda7a (qr_subq_exec+0x94a)
#6 0x756631 (ins_call+0xc91)
#7 0x758020 (ins_call_vec+0x320)
#8 0x75b835 (code_vec_run_v+0xa25)
#9 0x7b980f (qn_input+0x38f)
#10 0x7b9cb6 (qn_send_output+0x236)
#11 0x82c49d (set_ctr_vec_input+0x99d)
#12 0x7b984e (qn_input+0x3ce)
#13 0x7cb03b (qr_exec+0x11db)
#14 0x7d89d6 (sf_sql_execute+0x11a6)
#15 0x7d94de (sf_sql_execute_w+0x17e)
#16 0x7e219d (sf_sql_execute_wrapper+0x3d)
#17 0xe2aa3c (future_wrapper+0x3fc)
#18 0xe3233e (_thread_boot+0x11e)
#19 0x7f7cd3cc0609 (start_thread+0xd9)
#20 0x7f7cd3a90353 (clone+0x43)
```
Virtuoso 7.2.12 crashes at `virtpcre_exec`
This is a GitHub Issue
repo:virtuoso-opensource
owner:openlink
Title : Virtuoso 7.2.12 crashes at `virtpcre_exec`
Issue date:

--- start body ---
Virtuoso 7.2.12 crashes at `virtpcre_exec`.

PoC:
```sql
SELECT REGEXP_REPLACE('a', 'a', 'a', 9999999999999999999.9999999999999999999e-1, 0, NULL);
```

Backtrace:
```
#0 0xf20edd (virtpcre_exec+0x11ad)
#1 0xc594d0 (bif_regexp_parse_impl+0x430)
#2 0x755674 (ins_call_bif+0xc4)
#3 0x763539 (code_vec_run_1+0xdf9)
#4 0x7b9841 (qn_input+0x3c1)
#5 0x7cda7a (qr_subq_exec+0x94a)
#6 0x756631 (ins_call+0xc91)
#7 0x758020 (ins_call_vec+0x320)
#8 0x75b835 (code_vec_run_v+0xa25)
#9 0x7b980f (qn_input+0x38f)
#10 0x7b9cb6 (qn_send_output+0x236)
#11 0x82c49d (set_ctr_vec_input+0x99d)
#12 0x7b984e (qn_input+0x3ce)
#13 0x7cb03b (qr_exec+0x11db)
#14 0x7d89d6 (sf_sql_execute+0x11a6)
#15 0x7d94de (sf_sql_execute_w+0x17e)
#16 0x7e219d (sf_sql_execute_wrapper+0x3d)
#17 0xe2aa3c (future_wrapper+0x3fc)
#18 0xe3233e (_thread_boot+0x11e)
#19 0x7f7cd3cc0609 (start_thread+0xd9)
#20 0x7f7cd3a90353 (clone+0x43)
```
--- end body ---
