pgsql: Be more wary about partially-valid LOCALLOCK data in RemoveLocal

pgsql: Be more wary about partially-valid LOCALLOCK data in RemoveLocal

Be more wary about partially-valid LOCALLOCK data in RemoveLocalLock().

RemoveLocalLock() must consider the possibility that LockAcquireExtended()
failed to palloc the initial space for a locallock's lockOwners array.
I had evidently meant to cope with this hazard when the code was originally
written (commit 1785acebf2ed14fd66955e2d9a55d77a025f418d), but missed that
the pfree needed to be protected with an if-test.  Just to make sure things
are left in a clean state, reset numLockOwners as well.

Per low-memory testing by Andreas Seltenreich.  Back-patch to all supported
branches.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/ba51774d87a2a0402628f7bd68295c0b2913cc25

Modified Files
--------------
src/backend/storage/lmgr/lock.c |    6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)