mod_proxy_http: follow up to r1829573: remain EBCDIC friendly.

Keep using ap_rgetline() as before r1829573, since ap_rgetline_core() is
EBCDIC agnostic.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1829657 13f79535-47bb-0310-9956-ffa450edef68