Another followup to "Adding low-pt tracking with region of interest"

@spagan @adimitri @npetters @goblirsc Unfortunately, this is another followup to !33769 (merged) (which crashed when trying to output low-pt tracks) and !34794 (merged) (which we realized did not output the tracks, just the vertices and an empty track container). There was a return statement in SiSPSeededTrackFinderRoI which was preventing low-pt tracks from being written out. This version of the code has been verified to output the same low-pt track (and vertex) information as a version of the code from before MR edits.