Make VideoManager non-crashing if thermal video receiver was not created

src/VideoManager/VideoManager.cc

@@ -117,8 +117,10 @@ VideoManager::setToolbox(QGCToolbox *toolbox)
 
     // FIXME: AV: I believe _thermalVideoReceiver should be handled just like _videoReceiver in terms of event
     // and I expect that it will be changed during multiple video stream activity
-    connect(_thermalVideoReceiver, &VideoReceiver::timeout, this, &VideoManager::_restartVideo);
-    connect(_thermalVideoReceiver, &VideoReceiver::streamingChanged, this, &VideoManager::_streamingChanged);
+    if (_thermalVideoReceiver != nullptr) {
+        connect(_thermalVideoReceiver, &VideoReceiver::timeout, this, &VideoManager::_restartVideo);
+        connect(_thermalVideoReceiver, &VideoReceiver::streamingChanged, this, &VideoManager::_streamingChanged);
+    }
 #endif
     _updateSettings();
     if(isGStreamer()) {