Move returning to editor to end of frame

This fixes horizontal and vertical warp backgrounds not resetting, and
also a bunch of other 1-frame glitches, most noticeably cutscene bars
and fadeouts.

This adds a new variable shouldreturntoeditor to Game to signal whether
or not it should return to editor at the end of the frame.

desktop_version/src/Logic.cpp

@@ -1380,4 +1380,12 @@ void gamelogic()
 
     if (game.teleport_to_new_area)
         script.teleport();
+
+#if !defined(NO_CUSTOM_LEVELS)
+    if (game.shouldreturntoeditor)
+    {
+        game.shouldreturntoeditor = false;
+        game.returntoeditor();
+    }
+#endif
 }