email template tags {{ITEM_THUMB}} and {{LOCATION_THUMB}} are not working

[poilu]

Thumbnails of items or locations are not included in emails. The very likely reason is that the responsible helper function doesn't return a value. https://github.com/wielebenwir/commons-booking/blob/44db9f620bb4229ab3874e55e0af9c0f89b64c79/includes/commons-booking-helpers.php#L139