mod_proxy_http: make use of AP_GETLINE_NOSPC_EOL in ap_proxygetline().

Fixes response header thrown away after the previous one was considered too
large and truncated.

PR 62196.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1829573 13f79535-47bb-0310-9956-ffa450edef68