In preparation for fixing issue #3362, reduce the side effects from calling
output_unified_flush_hunk() in the file based unified diff producer.

* subversion/libsvn_diff/diff_file.c
  (output_unified_flush_hunk): Don't use baton as local temporary variable.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1437444 13f79535-47bb-0310-9956-ffa450edef68