Better handle the case where ProxyBadHeader StartBody is

in effect and we think we've started reading in the
response body. Take advantage of the fact that the
line read is still in buffer (and document that)
to allow us to add to the bb.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@151722 13f79535-47bb-0310-9956-ffa450edef68