wallet: Assert that enough was selected to cover the fees
wallet: Assert that enough was selected to cover the fees

When the fee is not subtracted from the outputs, the amount that has
been reserved for the fee (change_and_fee - change_amount) must be
enough to cover the fee that is needed. It would be a bug to not do so,
so use an assert to make this obvious if such a situation were to occur.

Github-Pull: bitcoin/bitcoin#22686
Rebased-From: d9262324e80da32725e21d4e0fbfee56f25490b1

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