Fix UseCanonicalCase off case where it'd improperly examine port number.

parsed_uri.port is only valid iff parsed_uri.port_str != NULL.
Old code simply checked if it was non-zero, not if it
was *valid*

Backport of server/core.c r1.248 from httpd-2.1
Submitted by:	Jim Jagielski
Reviewed by:	Brad Nicholes, Jim Jagielski, Justin Erenkrantz


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/APACHE_2_0_BRANCH@102116 13f79535-47bb-0310-9956-ffa450edef68