pgsql: ecpg: Fix NULL pointer dereference during connection lookup

ecpg: Fix NULL pointer dereference during connection lookup

ECPGconnect() caches established connections to the server, supporting
the case of a NULL connection name when a database name is not specified
by its caller.

A follow-up call to ECPGget_PGconn() to get an established connection
from the cached set with a non-NULL name could cause a NULL pointer
dereference if a NULL connection was listed in the cache and checked for
a match. At least two connections are necessary to reproduce the issue:
one with a NULL name and one with a non-NULL name.

Author: Aleksander Alekseev <aleksander(at)tigerdata(dot)com>
Discussion: https://postgr.es/m/CAJ7c6TNvFTPUTZQuNAoqgzaSGz-iM4XR61D7vEj5PsQXwg2RyA@mail.gmail.com
Backpatch-through: 13

Branch
------
REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/313d3102facdc61317d1292ab8f2d6cf1f254282

Modified Files
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src/interfaces/ecpg/ecpglib/connect.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)