Removed redundant initialization of GrayscaleRenderOptions

Removed the initialization of a `GrayscaleRenderOptions` instance in the
`FromDataset` method, since complete `GrayscaleRenderOptions` objects are
returned from every path of the `if`- `else` code block. With this code
removal, an annoying **unreachable code detected** warning during build
can be avoided.

Colby, I hope you find this update worthwhile pulling into the main repository.

Best regards,
Anders @ Cureos