Fix a bug in the marshalling of errors with no messages.  Since we can't easily change the message to be optional, marshal NULL messages as "".
Fix a bug in the marshalling of errors with no messages.  Since we
can't easily change the message to be optional, marshal NULL
messages as "".

* libsvn_ra_svn/marshal.c:
  (svn_ra_svn_write_cmd_failure): Marshal NULL messages as "".
  (svn_ra_svn_read_cmd_response): Unmarshal "" messages to NULL.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@849367 13f79535-47bb-0310-9956-ffa450edef68

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