Fix a segfault when trying to follow the history of a file and we traverse a revision that has no changes in it.  E.G.:
Fix a segfault when trying to follow the history of a file and we traverse a
revision that has no changes in it.  E.G.:

svn diff -r3078:3079 http://svn.collab.net/repos/svn

Bug found by Øyvind A. Holm

* subversion/libsvn_client/ra.c
  (log_receiver): When changed_paths is NULL, nothing to do.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@850442 13f79535-47bb-0310-9956-ffa450edef68

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