Convert a lot of apr_ssize_t to apr_size_t. We don't ever accept or return

signed values in these integers, and we return the error codes directly,
so we should always report the number of bytes read/written correctly.  If
we have an error, that is 0 bytes.  If that is true, then using signed
values doesn't make any sense.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86857 13f79535-47bb-0310-9956-ffa450edef68