session-lock: send more protocol errors

The invalid_destroy and invalid_unlock protocol errors aren't currently
sent by wlroots and instead left up to the compositor. However, we can
handle these as well without much additional complexity.

This also adds a missing wl_resource_destroy() call if the lock is inert
in lock_handle_unlock_and_destroy().

include/wlr/types/wlr_session_lock_v1.h

@@ -40,6 +40,10 @@ struct wlr_session_lock_v1 {
 	} events;
 
 	void *data;
+
+	// private state
+
+	bool locked_sent;
 };
 
 struct wlr_session_lock_surface_v1_state {