- Fix up a comment so that it makes more sense and explains why we return

- Fix up a comment so that it makes more sense and explains why we return
  APR_EOF instead of an EOS bucket.
- Start to try to be nice when we *know* we are EOS by removing the
  bucket.  This is only one case where we could end up with a 0 bucket
  in ctx->b, but let's remove it and move on.  (If the bucket were to
  return 0 bytes and still have data left to read on blocking mode,
  it's blantly broken, IMHO)

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@93270 13f79535-47bb-0310-9956-ffa450edef68