Avoid access to already-released lock in LockRefindAndRelease.

Spotted by Tom Lane.

src/backend/storage/lmgr/lock.c

@@ -2949,7 +2949,7 @@ LockRefindAndRelease(LockMethod lockMethodTable, PGPROC *proc,
 	 * Decrement strong lock count.  This logic is needed only for 2PC.
 	 */
 	if (decrement_strong_lock_count
-		&& ConflictsWithRelationFastPath(&lock->tag, lockmode))
+		&& ConflictsWithRelationFastPath(locktag, lockmode))
 	{
 		uint32		fasthashcode = FastPathStrongLockHashPartition(hashcode);