Enable returning to Secret Lab immediately from Super Gravitron

When you enter the Super Gravitron, you have to wait until the Super
Gravitron actually starts before being able to press Enter to return to
the Secret Lab. This is annoying if you just want to get back to the
Secret Lab. So, I've made it so the press-Enter-to-return functionality
is enabled from the moment that the Super Gravitron starts.

desktop_version/src/Input.cpp

@@ -2064,7 +2064,8 @@ void gameinput(void)
     {
         // Do nothing
     }
-    else if (game.swnmode == 1 && game.swngame == 1)
+    else if (game.swnmode == 1
+    && (game.swngame == 1 || game.swngame == 6 || game.swngame == 7))
     {
         //quitting the super gravitron
         game.mapheld = true;