Fix customer status flow in unilateral closes

[marsella]

Right now, the customer status flow when the merchant posts expiry is

1. Immediately enter PendingClose
2. Enter PendingExpiry if they don't have updated balances
3. otherwise stay in PendingClose

But the spec says it should

1. Immediately enter PendingExpiry
2. Enter PendingClose if they do have updated balances
3. otherwise stay in PendingExpiry

I think this should be fixed so that we

• avoid a weird race condition if something else happens between 1 and 2
• can more easily update the code if we change the contract to support mutual close from an expiry state