Initialize 'recordXtime' to silence compiler warning.

In reality, recordXtime will always be set by the getRecordTimestamp
call, but the compiler doesn't necessarily see that.

Back-patch to all supported versions.

Author: Tristan Partin
Discussion: https://www.postgresql.org/message-id/CT5MN8E11U0M.1NYNCHXYUHY41@gonk

Author: hlinnaka

src/backend/access/transam/xlogrecovery.c

@@ -2644,7 +2644,7 @@ recoveryStopsAfter(XLogReaderState *record)
 	uint8		info;
 	uint8		xact_info;
 	uint8		rmid;
-	TimestampTz recordXtime;
+	TimestampTz recordXtime = 0;
 
 	/*
 	 * Ignore recovery target settings when not in archive recovery (meaning