For NewFile(), Use Interface instead of Concrete Class

[kenssamson]

https://github.com/techyian/MMALSharp/blob/1e245e0283146ae4219c7ec0286568cda11bc4ed/src/MMALSharp/Callbacks/FastImageOutputCallbackHandler.cs#L55-L58

NewFile() is defined in the interface IFileStreamCaptureHandler. This code should use that interface instead of using the derived concrete class ImageStreamCaptureHandler.

For example:

if (eos && this.CaptureHandler is IFileStreamCaptureHandler)
{
    ((IFileStreamCaptureHandler)this.CaptureHandler).NewFile();
}

This would allow users to create a custom IFileStreamCaptureHandler that uses a different naming scheme without having to overwrite the PostProcess code.

[techyian]

Thanks Ken. I've fixed this now.