Merge r1646282 from trunk:

* Fix If-Match handling:
  - We need to fail if we do NOT match.
  - ETag comparison only makes sense if we have an ETag

PR: 57358
Submitted by: Kunihiko Sakamoto <ksakamoto google.com>
Reviewed by: rpluem

Submitted by: rpluem
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1674658 13f79535-47bb-0310-9956-ffa450edef68