Set color space in input image prior to resample.

[MarkCallow]

Fixes #1050.

[aqnuep]

@MarkCallow, we did not implement scaling, so I have no idea whether this is the right order of operations, therefore I'm not sure I can provide an informed review of this without understanding the details how scaling was added.

[MarkCallow]

@MarkCallow, we did not implement scaling, so I have no idea whether this is the right order of operations, therefore I'm not sure I can provide an informed review of this without understanding the details how scaling was added.

Thanks for looking. --generate-mipmap is also affected by this bug as both it and --scale use the resample method to resize images. Not having the color space set before scaleImage and generateMipLevels are called results in Image::resample always seeing _UNSPECIFIED and so never decoding sRGB images. The color space must be set before these functions are called. I am confident this is the correct order so I am going to merge this.

I am not too surprised the issue was missed when the --generate-mipmap tests were added as the differences between correct and incorrect images are very subtle.