Fix warnings

src/FlightDisplay/VideoManager.cc

@@ -32,8 +32,8 @@ QGC_LOGGING_CATEGORY(VideoManagerLog, "VideoManagerLog")
 //-----------------------------------------------------------------------------
 VideoManager::VideoManager(QGCApplication* app, QGCToolbox* toolbox)
     : QGCTool(app, toolbox)
-    , _videoReceiver(NULL)
-    , _videoSettings(NULL)
+    , _videoReceiver(nullptr)
+    , _videoSettings(nullptr)
     , _fullScreen(false)
 {
 }

src/VideoStreaming/VideoReceiver.h

@@ -44,7 +44,7 @@ public:
     Q_PROPERTY(QString          videoFile           READ    videoFile           NOTIFY  videoFileChanged)
     Q_PROPERTY(bool             showFullScreen      READ    showFullScreen      WRITE   setShowFullScreen     NOTIFY showFullScreenChanged)
 
-    explicit VideoReceiver(QObject* parent = 0);
+    explicit VideoReceiver(QObject* parent = nullptr);
     ~VideoReceiver();
 
 #if defined(QGC_GST_STREAMING)