Fix two potential merge.c segfaults.
Fix two potential merge.c segfaults.

* subversion/libsvn_client/merge.c
  (insert_child_to_merge): Copy cached propval member too when manipulating
   array of merge_path_t *s.
  (do_merge, cleanup_noop_merge): Handle NULL items in
  children_with_mergeinfo, as this is possible since r26243.
  


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@866454 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion