Fix bug: Unable to skip credits in certain cases

If you had the map button held before the game transitioned to the
credits and ending picture sequences, then you wouldn't be able to skip
them, because those gamemodes don't have logic to detect when you've
released the map button.

To fix this, just implement the map button release logic.

We do need a better input system soon...

desktop_version/src/Input.cpp

@@ -3327,6 +3327,11 @@ void gamecompleteinput(void)
             }
         }
     }
+
+    if (!game.press_map)
+    {
+        game.mapheld = false;
+    }
 }
 
 void gamecompleteinput2(void)
@@ -3368,4 +3373,9 @@ void gamecompleteinput2(void)
             }
         }
     }
+
+    if (!game.press_map)
+    {
+        game.mapheld = false;
+    }
 }