[fix] non-media items trumped upnp listings, fixes #14268

This fixes a silly bug introduced in e9dab0. When a non-media item (class == object.item) was discovered it reset a variable used for a completely different check (which media items to show). This only affected 'files' views (ie listings containing non-media items) for servers other than XBMC, hence me not noticing it.

I've reverted to using a string compare instead of trumping the booleans.

This is not needed for Gotham as the bug was squashed in a refactor by elupus.