gitweb: escape html in rss title

The title of an RSS feed is generated from many components,
including the filename provided as a query parameter, but we
failed to quote it.  Besides showing the wrong output, this
is a vector for XSS attacks.

Signed-off-by: Jeff King <peff@peff.net>

gitweb/gitweb.perl

@@ -8055,6 +8055,7 @@ sub git_feed {
 		$feed_type = 'history';
 	}
 	$title .= " $feed_type";
+	$title = esc_html($title);
 	my $descr = git_get_project_description($project);
 	if (defined $descr) {
 		$descr = esc_html($descr);