Backport

Merge r1749151 from trunk:

mod_http2: fix for request abort when connections drops, introduced in 1.5.8
Submitted by: icing
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1749331 13f79535-47bb-0310-9956-ffa450edef68