gitadora: (arena model) fix window settings not working (#494)

## Link to GitHub Issue, if one exists
#477 

## Description of change
F11 menu (window settings) did not work for arena model because the game
engine races to create many windows, so our logic of grabbing the first
window created doesn't always get the main window.

## Testing

src/spice2x/overlay/windows/screen_resize.cpp

@@ -27,6 +27,11 @@ namespace overlay::windows {
     }
 
     HWND ScreenResize::get_first_window() {
+        // hack for gitadora arena model which races to create many windows
+        // so [0] is not always the main one
+        if (GRAPHICS_WINDOW_MAIN.has_value()) {
+            return GRAPHICS_WINDOW_MAIN.value();
+        }
         if (GRAPHICS_WINDOWS.size() == 0) {
             return NULL;
         }