Check for presence of user metadata subset

[mojodna]

Some PBFs may contain partial metadata without empty values for uid, user, and changeset. This prevents an IndexOutOfBoundsException when attempting to read such files.

I don't know how to generate such a PBF for a test fixture (and Peru is too large), so swapping in http://download.geofabrik.de/south-america/peru-180101.osm.pbf for data-with-metadata.pbf will trigger the bug in TestReadWithMetadata.