backporting from 2.1:

  *) Fix mod_deflate so that it does not call deflate() without checking
     first whether it has something to deflate. (Currently this causes
     deflate to generate a fatal error according to the zlib spec.)
     PR 22259.
PR:
Obtained from:
Submitted by:
Reviewed by:


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/APACHE_2_0_BRANCH@100986 13f79535-47bb-0310-9956-ffa450edef68