Merge pull request #1 from BradLarson/master

Update of my fork
Fixed an issue that caused an app crash if the processing of the video was cancelled right after it started. This caused the assetWriter of the GPUImageMovieWriter to be in an unknown state instead of a cancelled state.
Merge pull request #1001 from jvaldera/master

Fixed an infrequent app crash when a video processing is cancelled.