SaveState: Show a warning if saved after savestate.

If you load a save state from before you created savedata (or from a
different path of savedata), some games will refuse to save.  This shows a
warning since it can be a confusing situation.

We could potentially add an undo for loading state, to give an option for
getting back after this warning.

Core/SaveState.h

@@ -100,6 +100,9 @@ namespace SaveState
 	// Check if there's any save stating needing to be done.  Normally called once per frame.
 	void Process();
 
+	// Notify save state code that new save data has been written.
+	void NotifySaveData();
+
 	// Cleanup by triggering a restart if needed.
 	void Cleanup();
 };