Backport r1031551

proxy_connect: Don't give up in the middle of a CONNECT tunnel
when the child process is starting to exit.  PR50220. [Eric Covener]


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@1043628 13f79535-47bb-0310-9956-ffa450edef68