fix: destroy wayland proxy before cleanup to prevent use-after-free crash

Call destroy() on the treeland_foreign_toplevel_handle_v1 proxy before emitting
handlerIsDeleted() to stop the compositor from sending further events to a handle
scheduled for C++ destruction. Without this, pending state events could arrive
after the ForeignToplevelHandle object is freed by QScopedPointer, causing a
crash in m_states.append() when activating applications from the system tray.

Author: LFRon

panels/dock/taskmanager/treelandwindow.cpp

@@ -108,6 +108,7 @@ void ForeignToplevelHandle::treeland_foreign_toplevel_handle_v1_done()
 }
 void ForeignToplevelHandle::treeland_foreign_toplevel_handle_v1_closed()
 {
+    destroy();
     Q_EMIT handlerIsDeleted();
 }