Merge r1556206 from trunk:

avoid a tight busy loop with memory allocations when the [N] flag
isn't making progress.

If backported, probably increase the hard-coded limit to 32k from 10k.


Submitted by: covener
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1562174 13f79535-47bb-0310-9956-ffa450edef68