Many thanks for spotting this. Now fixed in changeset 70f0280c07a8.

For anybody patching a 1.5.0 system there is also another missing " three lines further on. Those lines in the else block should look like this:

~~~~
{
// Put the date into a data attribute so that it can be picked up by JavaScript
$header_inner .= '' .
'' .
utf8_strftime($dformat, $t) . "
\n";
}
~~~~