phabricator: fallback to reading metadata from diff for phabread
Differential Revision: https://phab.mercurial-scm.org/D6301
{header}
<title>Error</title>
<description>Error</description>
<item>
<title>Error</title>
<description>{error|escape}</description>
<guid>https://mercurial-scm.org/#error</guid>
</item>
</channel>
</rss>