Fix a segfault when performing an --ignore-ancestry file merge.

See http://svn.haxx.se/dev/archive-2013-03/0252.shtml

* subversion/libsvn_client/merge.c
  (do_file_merge): Initialize MERGE_TARGET outside of block which is
   dependent on mergetracking, as that local variable is referenced
   regardless of whether mergetracking is happening.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1457046 13f79535-47bb-0310-9956-ffa450edef68