Skip missing placeholders

[MGatner]

Verifying matches (MenusFilter:81):

// Swap the content for the placeholder and verify a match
$body = str_replace('{{' . $alias . '}}', $content, $body, $count);
if ($count === 0)
{
	throw new RuntimeException('Missing placeholder text for menu: ' . $alias);
}

... is turning out to be too punishing. If the placeholder is not located the filter should just ignore it, or maybe put a debug log entry.