libtracker-miner: Always fallback to URN query when queueing file

Tracker may end up with nfo:FileDataObject prior to handling monitor
events. Be it leftover data from previous bugs, explicit "tracker index"
calls, or data from some other application.

As we can't be really sure of the data consistence, always fallback to
a URN query so we don't break nie:url UNIQUE constraint (inverse functional
property in SPARQL parlance).

https://bugzilla.gnome.org/show_bug.cgi?id=786132