Notify viewers when channels close and refresh resumed playback state

tools/chatgui/transport/stream_bridge.cpp

@@ -155,7 +155,7 @@ bool gui_stream_attach(UTUN_INSTANCE* inst) {
 
 void gui_stream_detach(UTUN_INSTANCE* inst) {
     std::lock_guard<std::mutex> guard(bridge.lock);
-    if (bridge.inst != inst) return;
+    if (!inst || bridge.inst != inst) return;
     if (bridge.pending) uasync_cancel_post(inst->ua, bridge.pending);
     bridge.pending = nullptr; stream_set_event_callback(inst, nullptr, nullptr);
     if (bridge.viewer.id) closeViewer(StreamRecordKind::Closed, STREAM_CLOSE_SERVICE);