In certain pathological cases related to in-progress upgrades of a

server, we may get into a situation where an entrypoint appears to

exist, but attempting to load it gives us empty metadata. Most of the

extension info code is written to handle when the metadata dict is

empty, but we were basing the htdocs path for media on whatever the

Name was, which would end up attempting to pass in None as an

argument to os.path.join(). This change updates it so we use the

extension ID as a fallback if the Name doesn't exist in the metadata.

Ran unit tests.