Fix a client-certificate bug in svn client.
Fix a client-certificate bug in svn client.

* libsvn_ra_dav/session.c (client_ssl_callback): if client-cert is
  unencrypted (has no password), go ahead and use it rather than exiting.  :-)


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@847720 13f79535-47bb-0310-9956-ffa450edef68

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