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/Input.cpp

@@ -1537,7 +1537,7 @@ void gameinput()
                    game.activeactivity = -1;
                }
             }else{
-                game.returntoeditor();
+                game.shouldreturntoeditor = true;
             }
         }
     }