List discussion resulted in rejecting all but SP characters in the request

line, but in the strict mode prioritize excessive space testing over bad
space testing (which is captured later) and make both more efficient
(at this test ll[0] is already a SP or NULL char). Also correct a comment.

Backports: r1770867
Submitted by: wrowe


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x-merge-http-strict@1770868 13f79535-47bb-0310-9956-ffa450edef68