Fix: Skip video capture when camera fails to open

CCaptureVideo::Open now returns S_FALSE when BindVideoFilter cannot bind a capture device, instead of S_OK. CVideoManager records the result in m_bVideoOpened and exits WorkThread before SendBitMapInfor, so a host without a webcam no longer sends a 0x0 BITMAPINFO to the controller.

Co-Authored-By: deepseek-v4-pro

client/VideoManager.h

@@ -25,6 +25,7 @@ public:
 
     BOOL  m_bIsWorking;
     HANDLE m_hWorkThread;
+    BOOL m_bVideoOpened;
 
     void SendBitMapInfor();
     BOOL SendNextScreen();