pgsql: Cope with heap_fetch failure while locking an update chain

Cope with heap_fetch failure while locking an update chain

The reason for the fetch failure is that the tuple was removed because
it was dead; so the failure is innocuous and can be ignored.  Moreover,
there's no need for further work and we can return success to the caller
immediately.  EvalPlanQualFetch is doing something very similar to this
already.

Report and test case from Andres Freund in
20131124000203.GA4403@alap2.anarazel.de

Branch
------
REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/fbface6f946242571f4acbfa9a74727c073748ba

Modified Files
--------------
src/backend/access/heap/heapam.c |   11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)