Instance location improperly determined

https://github.com/googlefonts/fontmake/blob/6a8b2907891537ce559dd3d6fcfe68d8b55d6bc9/Lib/fontmake/instantiator.py#L356

This accesses `instance.location` instead of calling getFullLocation or whatsitcalled. Instances with a label instead of an old-school location will be placed at the default location. The instantiator should probably remember the labels of the DS and use them, or keep a reference to the DS to be able to resolve locations...