Supplying a manifest with an invalid `paintedResource.asset.id` returns 500

[griffri]

Supplying an invalid asset to a painted resource should return a dlcsException error, but if the id is set to an invalid value - e.g:

• "https://presentation-api.dlcs.digirati.io/52/canvases/random_resource_ooETA0", which I supplied by mistake
• "")

...Presentation will instead return a vague 500 error.