Follow-up to r1618616: fix build

* subversion/libsvn_client/merge.c
  (merge_file_opened, merge_dir_opened): Look for merge-left node kind in
   the right place.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1618617 13f79535-47bb-0310-9956-ffa450edef68