pgsql: reorderbuffer: preserve errno while reporting error

reorderbuffer: preserve errno while reporting error

Clobbering errno during cleanup after an error is an oft-repeated, easy
to make mistake. Deal with it here as everywhere else, by saving it
aside and restoring after cleanup, before ereport'ing.

In passing, add a missing errcode declaration in another ereport() call
in the same file, which I noticed while skimming the file looking for
similar problems.

Backpatch to 9.4, where this code was introduced.

Branch
------
REL9_6_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/0440f49523fb88a3ecbc1672d8fcee20197c5c40

Modified Files
--------------
src/backend/replication/logical/reorderbuffer.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)