PS-4989: Fixing innodb_track_changed_pages debug validation

In debug builds, this setting is allowed to be turned off temporarily after it was
turned on during startup. Howewer memory garbage also caused it to be accidentally
turned on when it was disabled at startup.

storage/xtradb/handler/ha_innodb.cc

@@ -19148,8 +19148,10 @@ innodb_track_changed_pages_validate(
 		return 0;
 	}
 
-	if (intbuf == srv_track_changed_pages)
+	if (intbuf == srv_track_changed_pages) { // == 0
+		*reinterpret_cast<ulong*>(save) = srv_track_changed_pages;
 		return 0;
+	}
 
 	return 1;
 }