minor cleanups in http_filter() and ap_get_client_block()

this is not the change to allow us to read broken-up header lines again :(

. http_filter()
  - respect apr_status_t as set by bucket->read() or ap_get_brigade()
  - return apr_status_t instead of length
. ap_get_client_block()
  - remove a confusing line which set the length parameter before
  - passing it to bucket->read()


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86517 13f79535-47bb-0310-9956-ffa450edef68