TrackerMinerFiles: Allow late addition of tracker:mountPoint.
TrackerMinerFiles: Allow late addition of tracker:mountPoint.

Since the URNs are now anonymous, we might not know yet the mount
point URN, so this data is added when the mount point GFile is
processed.

hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker,hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker