Fix nullptr dereference on A/V timeout

src/core/coreav.cpp

@@ -236,9 +236,12 @@ void Core::cleanupCall(int32_t callId)
     {
         delete calls[callId].camera;
         calls[callId].camera = nullptr;
+        if (calls[callId].videoSource)
+        {
             calls[callId].videoSource->setDeleteOnClose(true);
             calls[callId].videoSource = nullptr;
         }
+    }
 
     Audio::unsuscribeInput();
     toxav_kill_transmission(Core::getInstance()->toxav, callId);