input: don't run modifier bindings when the kbd is grabbed

We don't want bindings to be run while the keyboard is grabbed.
Otherwise the binding handler may grab the keyboard too, making
the old grab go away without even being cancelled.

src/bindings.c

@@ -293,6 +293,9 @@ weston_compositor_run_modifier_binding(struct weston_compositor *compositor,
 {
 	struct weston_binding *b;
 
+	if (seat->keyboard->grab != &seat->keyboard->default_grab)
+		return;
+
 	wl_list_for_each(b, &compositor->modifier_binding_list, link) {
 		weston_modifier_binding_handler_t handler = b->handler;