Errors in add-ons tab don't allow updating the product and don't show error

[Valentina R]

If there is some missing field/error in the add-ons tab, one can't update the product. There is no error shown unless you manually go to the add-ons tab.

Reported here: https://bookingwp.com/forums/topic/cant-update-page-with-plug-in-on/

[Željan Topić]

When no JS errors are available, it should prevent customer to save product options and scroll to the add-on error in place.