Remove bogus while-loop.

Commit abf5c5c9a4f142b3343614746bb9e99a794f8e7b added a bogus while-
statement after the for(;;)-loop. It went unnoticed in testing, because
it was dead code.

Report by KONDO Mitsumasa. Backpatch to 9.3. The commit that introduced
this was also applied to 9.2, but not the bogus while-loop part, because
the code in 9.2 looks quite different.

src/backend/access/transam/xlog.c

@@ -11333,9 +11333,9 @@ WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess,
 		 * process.
 		 */
 		HandleStartupProcInterrupts();
-	} while (StandbyMode);
+	}
 
-	return false;
+	return false; 	/* not reached */
 }
 
 /*