Обсуждение: pgsql: Fix DetermineSafeOldestOffset for the case where there are no mx

Fix DetermineSafeOldestOffset for the case where there are no mxacts.

Commit b69bf30b9bfacafc733a9ba77c9587cf54d06c0c failed to take into
account the possibility that there might be no multixacts in existence
at all.

Report by Thomas Munro; patch by me.

Branch
------
REL9_4_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/7b3f0f8b8ac2278d29e39b685d7c84ccd6ce1e93

Modified Files
--------------
src/backend/access/transam/multixact.c |   23 +++++++++++++++++------
1 file changed, 17 insertions(+), 6 deletions(-)