Maya: fix model publishing

[antirotor]

Model publishing was broken when no sets were found during extraction of model render sets. It will bail out now if no sets are found.

[tokejepsen]

Should this not be a validator?

[mkolar]

Actually it's a mechanism that works on a model when the data is available and shouldn't work when it isn't so probably not best as validator

[davidlatwe]

Linking the original PR that produce this bug : #1955

Cannot test this at the moment, but I think maybe we should modify the ExtractModelRenderSets class's process method instead ?

Like :

class ExtractModelRenderSets(ExtractLook):
    def process(self, instance):
        lookdata = instance.data["lookData"]
        relationships = lookdata["relationships"]
        sets = relationships.keys()
        if sets:
            return super(ExtractModelRenderSets, self).process(instance)
        else:
            self.log.info("No sets found")
            return

I can sumit another PR for this if you agree. :)

[antirotor]

Yeah, but - even for look extraction - empty set is bad thing there too, isn't it? I know it shouldn't get there because of validators...

[davidlatwe]

That's true :P

Adding more context here, linking the validator that validates on family look 👇🏼
https://github.com/pypeclub/OpenPype/blob/7ab4d0d6a38f71b0a8cdb7e23fd503541888f227/openpype/hosts/maya/plugins/publish/validate_look_contents.py#L73-L76

In this case is the family model borrowing look's extractor for optional extra data (rendering sets), and model doesn't run through the above look content validator hence the bug.

But yeah, empty set is bad for look as well. Like the simplicity of this PR.