Ticket URL not rendering in twig when imported from feed

If you import a feed that specifies an external ticket URL (X-TICKETS-URL), the ticket_url twig variable is not available which causes the ticket button to not render in the event-single.twig template using {{ticket_url}}. This is because of an error in this conditional https://github.com/thenly/all-in-one-event-calendar/blob/6da992d20be8d4f75b961fb71868d7e25969b78b/app/view/event/single.php#L132 . Commenting out this line makes event-single.twig render correctly. I suspect this was caused by the addition of the newer Time.ly ticket purchasing feature.

Version 2.5.12

Template: https://github.com/thenly/all-in-one-event-calendar/blob/6da992d20be8d4f75b961fb71868d7e25969b78b/public/themes-ai1ec/vortex/twig/event-single.twig#L15

Issue: https://github.com/thenly/all-in-one-event-calendar/blob/6da992d20be8d4f75b961fb71868d7e25969b78b/app/view/event/single.php#L132