More work on issue #510: 
More work on issue #510: 

* subversion/libsvn_delta/default_editor.c
  (apply_text): Allow for null handler.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@844719 13f79535-47bb-0310-9956-ffa450edef68

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