url.pm: Unicode C1 block characters in `\url` crash texml

[davidmjones]

This document results in a "error : string is not in UTF-8" warning and "No XML was generated: Could not create url-bug.xml: i18n error : output conversion failed due to conv error, bytes 0xFF 0x22 0x3E 0xC3
I/O error : encoder error" when the XML is being serialized.

%% AMS prddvilualatex

\documentclass{amsart}

\csname noTeXMLhistory\endcsname

\usepackage{url}

\title{hello}

\begin{document}

\maketitle

hello, world

\url{ÿ}

\end{document}