Reading a zipped crate that contains another RO-Crate picks up the wrong metadata

When reading a zip file with a structure:
```
/ro-crate-metadata.json
/a_directory/ro-crate-metadata.json
```

the inner `/a_directory/ro-crate-metadata.json` metadata file is (always?) used, due to the reader doing a depth-first search to find the metadata file.

