Avoid double-rendering on resize

On Windows and macOS, resizing the window with the mouse blocks the
event loop until the click is released. To keep rendering during
resizing, an event watcher is registered to handle resize events.

Avoid handling resize events twice by ensuring
`SDL_EVENT_WINDOW_PIXEL_SIZE_CHANGED` is processed only once.

PR #6758 <https://github.com/Genymobile/scrcpy/pull/6758>

app/src/screen.c

@@ -935,9 +935,12 @@ sc_screen_handle_event(struct sc_screen *screen, const SDL_Event *event) {
         case SDL_EVENT_WINDOW_EXPOSED:
             sc_screen_render(screen, true);
             return;
+// If defined, then the actions are already performed by the event watcher
+#ifndef CONTINUOUS_RESIZING_WORKAROUND
         case SDL_EVENT_WINDOW_PIXEL_SIZE_CHANGED:
             sc_screen_on_resize(screen);
             return;
+#endif
         case SDL_EVENT_WINDOW_RESTORED:
             if (screen->video && is_windowed(screen)) {
                 apply_pending_resize(screen);