When distribution contentType and File contentType mismatch, silently fails

[ssssarah]

This is a bit particular, but if a resource indicates having a distribution, but the distribution's contentType doesn't match the File's and the content type that is provided to forge.download has been inspired by the distribution's wrong contentType, forge will loop over all files' actual metadata, find nothing and download nothing.

https://github.com/BlueBrain/nexus-forge/blob/master/kgforge/core/archetypes/read_only_store.py#L132