qmol_from_ctab() with NULL crashes engine

[robins]

Describe the bug
Calling function qmol_from_ctab() with bogus string + a crafted NULL crashes the engine.

To Reproduce
SELECT qmol_from_ctab('a'::cstring, FALSE) <@ NULL::mol;

Expected behavior
As with #3687 ideally I'd expect the engine to not crash.

Screenshots / Output

psql (14devel, server 12.4)
Type "help" for help.

postgres=> select version();
                                                 version
---------------------------------------------------------------------------------------------------------
 PostgreSQL 12.4 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-11), 64-bit
(1 row)

postgres=> select rdkit_version();
 rdkit_version
---------------
 0.74.0
(1 row)

postgres=> SELECT qmol_from_ctab('a'::cstring, FALSE) <@ NULL::mol;
server closed the connection unexpectedly
        This probably means the server terminated abnormally
        before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.
!?>

Configuration (please complete the following information):

• RDKit version: 0.74.0

Additional context

• As with fmcs() + bogus input causes engine crash #3687 this is easily reproducible / forces an engine crash without warning.

Error Log excerpt

2021-01-04 07:50:51 UTC::@:[20623]:LOG: server process (PID 5097) was terminated by signal 11: Segmentation fault
2021-01-04 07:50:51 UTC::@:[20623]:DETAIL: Failed process was running: SELECT qmol_from_ctab('a'::cstring, FALSE) <@ NULL::mol;
2021-01-04 07:50:51 UTC::@:[20623]:LOG: terminating any other active server processes

[greglandrum]

Confirmed.
Curiously it doesn't happen with mol_from_ctab:

regression=# select mol_from_ctab('a'::cstring,False)<@NULL::mol;
WARNING:  could not create molecule from CTAB 'a'
 ?column? 
----------
 
(1 row)