BradLarson/GPUImage — pull request #1613 by mmtootmm (2014-06-11 10:38:41+00:00)
Title: Fixed realtime video recording

When realtime video recording, `newFrameReadyAtTime:atIndex:` and `startRecording` in GPUImageMovieWriter may be called on other thread.
So `startWriting` in `startRecording` called after `startWriting` in `newFrameReadyAtTime:atIndex:` sometime.
It causes error.
Setting `isRecording` to `YES` after finished `startRecording` fixes issue.