Improve quit-to-menu menu handling

This stabilizes the code that handles the menu that you land on if you
press Esc and quit to the menu.

Instead of using Game::returnmenu(), we now use the new function
Game::returntomenu() to clearly express intent that we want to return to
a specific menu. So I've added another kludge variable
Game::wasinintermission for the was-in-intermission case.

Also, I made it so that if you didn't have a main game telesave or
quicksave, you just get brought back to the main menu. Because you
shouldn't be able to go to the play menu without a quicksave or
telesave.

desktop_version/src/editor.cpp

@@ -3471,10 +3471,7 @@ void editorlogic()
         map.nexttowercolour();
         ed.settingsmod=false;
         graphics.backgrounddrawn=false;
-        //Do returnmenu twice because we have two menus:
-        //the main editor menu and the confirm save&quit menu
-        game.returnmenu();
-        game.returnmenu();
+        game.returntomenu(Menu::playerworlds);
     }
 }