Disable "resize to fit" in maximized state

In maximized state (but not fullscreen), it was possible to resize to
fit the device screen (with Ctrl+x or double-clicking on black borders).

This caused problems on macOS with the "expand to fullscreen" feature,
which behaves like a fullscreen mode but is seen as maximized by SDL.
In that state, resizing to fit causes unexpected results.

To keep the behavior consistent on all platforms, just disable "resize
to fit" when the window is maximized.

app/src/screen.c

@@ -484,15 +484,10 @@ screen_switch_fullscreen(struct screen *screen) {
 
 void
 screen_resize_to_fit(struct screen *screen) {
-    if (screen->fullscreen) {
+    if (screen->fullscreen || screen->maximized) {
         return;
     }
 
-    if (screen->maximized) {
-        SDL_RestoreWindow(screen->window);
-        screen->maximized = false;
-    }
-
     struct size optimal_size =
         get_optimal_window_size(screen, screen->content_size);
     SDL_SetWindowSize(screen->window, optimal_size.width, optimal_size.height);