Colorspace now allows empty file representation list

[jrsndl]

Changelog Description

Colorspace.py now check for empty file representation list.

Testing notes:

1. In Nuke, make sure render work folder (staging dir) has no rendered frames
2. Try to publish on farm with existing frames
3. Publisher should stop on rendered frames validatior, not on colorspace error

Can fix #97
Might also fix #66

[BigRoy]

This logic is wrong unfortunately. files may be a single filename str... so we'd still need the list check at least.

Suggested change

	filename = representation["files"][0] if representation["files"] else None
	filename = representation["files"]
	if isinstance(filename, list):
	if filename:
	filename = filename[0]
	else:
	filename = None

However, I really don't think this is the best fix here. We're suddenly allowing this to continue in a way where it may not be sensible to actually continue. I think this erroring is correct and hence we should handle the error elsewhere instead.

[jrsndl]

My intention is just to pass the error to validator that is working properly, with message that artist can understand.

[BigRoy]

The intention is good I think - but I think it makes more sense for collect_writes.py to NOT set representation colorspace IF there are no files if apparently, it cannot? Or at least capture it accordingly instead of silently ignoring it here where it we're expecting it to just work... instead of ignore silently?

[iLLiCiTiT]

The filename is needed only if colorspace is None so we should move it under the condition. And we should not set it to None as that would cause crash in get_imageio_file_rules_colorspace_from_filepath.