GPUImage 报错reason: 'Incomplete filter FBO: 36055'

Crash on videos without sound!
fixed:

AVAsset *anAsset = [AVAsset assetWithURL:_dictInfo[UIImagePickerControllerMediaURL]];
AVAssetTrack *assetTrack = [[anAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
_movieFile = [[GPUImageMovie alloc] initWithAsset:anAsset];
_movieWriter = [[GPUImageMovieWriter alloc] initWithMovieURL:_URLInputVideoFile size:assetTrack.naturalSize];

        if ([[anAsset tracksWithMediaType:AVMediaTypeAudio] count] > 0){            _movieFile.audioEncodingTarget = _movieWriter;        } else {//no audio            _movieFile.audioEncodingTarget = nil;        }

https://github.com/BradLarson/GPUImage/issues/1276#issuecomment-39695145

如果设置为nil，录制的视频将会没有声音。