Address form can't unset a State when editing

[ghost]

Description

I've tested this with your sample templates to make sure it wasn't something I'd done.

If you have an address with a state, say US and Florida, then if you come to edit the record and change country to somewhere that doesn't require a state, say UK, then when you save the record still shows Florida as the selected state.

The only way it works is to put a non null string in the 'stateName' field, which isn't ideal.

Not sure when the state fields switched to using stateValue instead of the separate stateId and stateName, but I find it messier this way.

Bug seems to stem from the if statement on line 476 of models/Address.php as an empty string or '0' evaluate to False and therefore the stateId and and stateName don't get changed.

Steps to reproduce

1. Create a new US address and select a State.
2. Save
3. Edit the address, set Country to one without state, e.g France.
4. Save.
5. The address still has the previously selected State

Additional info

• Craft version: 3.3.16.3
• PHP version: 7.3.11
• Database driver & version: MySQL 5.7.27
• Plugins & versions: Craft Commerce 2.2.8

[lukeholder]

Fixed as above.