Problem with mgvideoreader

[alexarje]

@benlyyan #bug

>> mg=mgvideoreader('pianist.mp4')
Error using VideoReader/init (line 619)
Could not read file due to an unexpected error. Reason: Unable to initialize the video obtain properties

Error in VideoReader (line 172)
            obj.init(fileName);

Error in mgvideoreader (line 29)
    obj = VideoReader(fn);