Smoothly interpolate "[Press ENTER to return to editor]" fadeout

Now it'll be real smooth at 60 FPS. Or above. Or whichever one you want
above 30.

desktop_version/src/Logic.cpp

@@ -1666,6 +1666,7 @@ void gamelogic()
     }
 
 #if !defined(NO_CUSTOM_LEVELS)
+    ed.oldreturneditoralpha = ed.returneditoralpha;
     if (map.custommode && !map.custommodeforreal && ed.returneditoralpha > 0)
     {
         ed.returneditoralpha -= 15;

desktop_version/src/Render.cpp

@@ -1389,7 +1389,8 @@ void gamerender()
 #if !defined(NO_CUSTOM_LEVELS)
      if(map.custommode && !map.custommodeforreal && !game.advancetext){
         //Return to level editor
-        graphics.bprintalpha(5, 5, "[Press ENTER to return to editor]", 220 - (help.glow), 220 - (help.glow), 255 - (help.glow / 2), ed.returneditoralpha, false);
+        int alpha = graphics.lerp(ed.oldreturneditoralpha, ed.returneditoralpha);
+        graphics.bprintalpha(5, 5, "[Press ENTER to return to editor]", 220 - (help.glow), 220 - (help.glow), 255 - (help.glow / 2), alpha, false);
       }
 #endif
 

desktop_version/src/editor.cpp

@@ -407,6 +407,7 @@ void editorclass::reset()
     script.customscripts.clear();
 
     returneditoralpha = 0;
+    oldreturneditoralpha = 0;
 
     ghosts.clear();
     currentghosts = 0;
@@ -4636,6 +4637,7 @@ void editorinput()
                         music.haltdasmusik();
                         graphics.backgrounddrawn=false;
                         ed.returneditoralpha = 1000; // Let's start it higher than 255 since it gets clamped
+                        ed.oldreturneditoralpha = 1000;
                         script.startgamemode(21);
                     }
                 }

desktop_version/src/editor.h

@@ -237,6 +237,7 @@ class editorclass{
   int dmtileeditor;
 
   int returneditoralpha;
+  int oldreturneditoralpha;
 
   std::vector<GhostInfo> ghosts;
   int currentghosts;