pgsql: In pg_log_generic(), be more paranoid about preserving errno.

In pg_log_generic(), be more paranoid about preserving errno.

This code failed to account for the possibility that malloc() would
change errno, resulting in wrong output for %m, not to mention the
possibility of message truncation.  Such a change is obviously
expected when malloc fails, but there's reason to fear that on some
platforms even a successful malloc call can modify errno.

Discussion: https://postgr.es/m/2576.1527382833@sss.pgh.pa.us

Branch
------
REL_12_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/cf665ad4c89eb9b20285dc04aec906d46ed810d2

Modified Files
--------------
src/common/logging.c | 2 ++
1 file changed, 2 insertions(+)