docchecker: remove naked except clause
This is fixing for 'naked except clause' check-code rule.
check-code has overlooked this, because a file isn't recognized as one
to be checked (this problem is fixed by subsequent patch).
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<!-- This is the second screen displayed during the install. -->
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta http-equiv="Content-Style-Type" content="text/css">
<title></title>
<style type="text/css">
p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Helvetica}
p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica; min-height: 14.0px}
</style>
</head>
<body>
<p class="p1">This is a prepackaged release of <a href="https://mercurial-scm.org/">Mercurial</a> for Mac OS X.</p>
<p class="p2"><br></p>
<br>
<p>
Please be sure to read the latest <a href="https://mercurial-scm.org/wiki/WhatsNew">release notes</a>.</p>
</body>
</html>