Fix a couple of problems related to large request bodies:

  http_filter() - this was referencing e->length even though e->length
    is sometimes -1 (if we have to read the socket bucket to get the
    next bit of the request body); now it does e->read() to force a
    socket need if required
  ap_get_client_block() - this was getting a brigade back with the
    desired amount of data (yeah, right) but only copying out the first
    bucket


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86573 13f79535-47bb-0310-9956-ffa450edef68