On X11, fix ModifiersChanged from xdotool

xdotool will update modifiers before Xkb will actually send event
updating them, thus the modifiers will be updating even before the
actual update, which is unfortunate.

Links: https://github.com/alacritty/alacritty/issues/7502

src/platform_impl/linux/x11/mod.rs

@@ -347,6 +347,7 @@ impl<T: 'static> EventLoop<T> {
             held_key_press: None,
             first_touch: None,
             active_window: None,
+            modifiers: Default::default(),
             is_composing: false,
         };