Fix incorrect assertion bound in WaitForLSN()

The assertion checking MyProcNumber used MaxBackends as the upper bound, but the procInfos array is allocated with size MaxBackends + NUM_AUXILIARY_PROCS. This inconsistency would cause a false assertion failure if an auxiliary process calls WaitForLSN(). Author: Xuneng Zhou <xunengzhou@gmail.com>

Author: akorotkov

src/backend/access/transam/xlogwait.c

@@ -321,7 +321,7 @@ WaitForLSN(WaitLSNType lsnType, XLogRecPtr targetLSN, int64 timeout)
 Assert(waitLSNState);
 
 /* Should have a valid proc number */
-Assert(MyProcNumber >= 0 && MyProcNumber < MaxBackends);
+Assert(MyProcNumber >= 0 && MyProcNumber < MaxBackends + NUM_AUXILIARY_PROCS);
 
 if (timeout > 0)
 {