Convert NeedsIdr member into an atomic variable with a getter

app/streaming/session.h

@@ -42,6 +42,8 @@ public:
 
     void flushWindowEvents();
 
+    bool getAndClearPendingIdrFrameStatus();
+
 signals:
     void stageStarting(QString stage);
 
@@ -145,7 +147,7 @@ private:
     SDL_Window* m_Window;
     IVideoDecoder* m_VideoDecoder;
     SDL_SpinLock m_DecoderLock;
-    bool m_NeedsIdr;
+    SDL_atomic_t m_NeedsIdr;
     bool m_AudioDisabled;
     bool m_AudioMuted;
     Uint32 m_FullScreenFlag;