Reimplement svn_checksum_empty_checksum().
Reimplement svn_checksum_empty_checksum().

* subversion/libsvn_subr/checksum.c
  (svn_checksum_empty_checksum):
    Do not use svn_checksum__from_digest() which would results in two
    checks of the checksum's kind.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1327716 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion