Variants block ordering if not given specific Availability dates

-- HikaShop version -- : 3.0.0
-- Joomla version -- : 3.6.5
-- PHP version -- : 7.x
-- Browser(s) name and version -- : various
-- Error-message(debug-mod must be tuned on) -- : no stock availalbe

Just upgraded to 3.0.0 and tried to use Variants on several items.

When we added variants to any item they wouldn't allow any ordering of the item (even though all qty fields were set to "Unlimited".

After spending a couple hours working on this I was able to track it down.

If you have ANY variants you MUST set the "Available from" and "to" date/time in order for the variant to work. Leaving those areas blank (in the variant and the main product) won't let you order any of the items. As soon as we entered dates in both fields for ALL the variants (on several products) they all worked fine.

Looks like maybe a bug?