Virtuoso 7.2.12 crashes at  `bif_rowvector_sort_imp` when calling the `ROWVECTOR_DIGIT_SORT` function.

Environment: Ubuntu 20.04, docker image `openlink/virtuoso-opensource-7:7.2.12`.

PoC:
```sql
SELECT ROWVECTOR_DIGIT_SORT('-99999999.99999999', 1, 1);
```

Backtrace:
```
#0 0xbba9a3 (bif_rowvector_sort_imp+0x1c3)
#1 0xbbc6ee (bif_rowvector_digit_sort+0x6e)
#2 0x755af4 (ins_call_bif+0xc4)
#3 0x75d882 (code_vec_run_v+0x25f2)
#4 0x7b9c8f (qn_input+0x38f)
#5 0x7ba136 (qn_send_output+0x236)
#6 0x82c91d (set_ctr_vec_input+0x99d)
#7 0x7b9cce (qn_input+0x3ce)
#8 0x7cb4bb (qr_exec+0x11db)
#9 0x7d8e56 (sf_sql_execute+0x11a6)
#10 0x7d995e (sf_sql_execute_w+0x17e)
#11 0x7e261d (sf_sql_execute_wrapper+0x3d)
#12 0xe29cec (future_wrapper+0x3fc)
#13 0xe315ee (_thread_boot+0x11e)
#14 0x7f90e0548609 (start_thread+0xd9)
#15 0x7f90e0318353 (clone+0x43)
```
Virtuoso 7.2.12 crashes with the `ROWVECTOR_DIGIT_SORT` function
This is a GitHub Issue
repo:virtuoso-opensource
owner:openlink
Title : Virtuoso 7.2.12 crashes with the `ROWVECTOR_DIGIT_SORT` function
Issue date:

--- start body ---
Virtuoso 7.2.12 crashes at  `bif_rowvector_sort_imp` when calling the `ROWVECTOR_DIGIT_SORT` function.

Environment: Ubuntu 20.04, docker image `openlink/virtuoso-opensource-7:7.2.12`.

PoC:
```sql
SELECT ROWVECTOR_DIGIT_SORT('-99999999.99999999', 1, 1);
```

Backtrace:
```
#0 0xbba9a3 (bif_rowvector_sort_imp+0x1c3)
#1 0xbbc6ee (bif_rowvector_digit_sort+0x6e)
#2 0x755af4 (ins_call_bif+0xc4)
#3 0x75d882 (code_vec_run_v+0x25f2)
#4 0x7b9c8f (qn_input+0x38f)
#5 0x7ba136 (qn_send_output+0x236)
#6 0x82c91d (set_ctr_vec_input+0x99d)
#7 0x7b9cce (qn_input+0x3ce)
#8 0x7cb4bb (qr_exec+0x11db)
#9 0x7d8e56 (sf_sql_execute+0x11a6)
#10 0x7d995e (sf_sql_execute_w+0x17e)
#11 0x7e261d (sf_sql_execute_wrapper+0x3d)
#12 0xe29cec (future_wrapper+0x3fc)
#13 0xe315ee (_thread_boot+0x11e)
#14 0x7f90e0548609 (start_thread+0xd9)
#15 0x7f90e0318353 (clone+0x43)
```
--- end body ---
