Factor out some duplicate code in find_last_merged_location().  No logical
change.

* subversion/libsvn_client/merge.c

  (short_circuit_mergeinfo_log): New.

  (find_last_merged_location): Call new helper.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1464647 13f79535-47bb-0310-9956-ffa450edef68