Fix clash between Gravitron start text and timer

There is a clash between the timer text and the "Survive for 60
seconds!" text. It's minor in English but it can be worse in other
languages (e.g. Polish).

So make the timer go away when that text is onscreen.

desktop_version/src/Render.cpp

@@ -2221,6 +2221,7 @@ void gamerender(void)
     && (!game.swnmode || game.swngame != SWN_SUPERGRAVITRON)
     && game.showingametimer
     && !roomname_translator::enabled
+    && (!game.swnmode || game.swngame != SWN_START_GRAVITRON_STEP_3)
     && !draw_return_editor_text)
     {
         const char* tempstring = loc::gettext("TIME:");