As noted by rpluem, r->protocol isn't const char *. Ensure the exit cases

As noted by rpluem, r->protocol isn't const char *. Ensure the exit cases
are pstrdup'ed. Note that r->protocol = "" is not in a return path.

Simplify the garbage-in protocol handling without consideration to 'strict'
settings. It is expected to be caused by an invalid raw SP in the URL.

Backports: r1773159 (with pstrdup enhancement)
Submitted by: rpluem, wrowe

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x-merge-http-strict@1773161 13f79535-47bb-0310-9956-ffa450edef68