Fixes entry parse if there is no URL

[naps62]

Parsing was failing if an entry had no defined URL. The parser was assuming it existed, and using it to expand all relative URLs

While it probably always exists for any well-made RSS feed, it won't be true if we're using something like Kill The Newsletter to convert emails to RSS

[gabrielpoca]

@naps62 could you squash before I merge it?

[naps62]

@gabrielpoca done