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. Testing Done: Ran unit tests.