fix: verification of melt quote with empty outputs

[thesimplekid]

Description

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@davidcaseria this should fix the ci issue on #596

Notes to the reviewers

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Suggested CHANGELOG Updates

CHANGED

ADDED

REMOVED

FIXED

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Checklist

• I followed the code style guidelines
• I ran just final-check before committing

[ok300]

When can a mint operation have no outputs?

[thesimplekid]

When can a mint operation have no outputs?

It can't that would fail the unbalanced check.

cdk/crates/cdk/src/mint/mint_nut04.rs

Lines 321 to 328 in 0731f9e

	// We check the total value of blinded messages == mint quote
	if amount != mint_quote.amount {
	return Err(Error::TransactionUnbalanced(
	mint_quote.amount.into(),
	mint_request.total_amount()?.into(),
	0,
	));
	}

and for swap

cdk/crates/cdk/src/mint/verification.rs

Lines 227 to 232 in 0731f9e

	if output_verification.amount
	!= input_verification
	.amount
	.checked_sub(fees)
	.ok_or(Error::AmountOverflow)?
	{

[ok300]

I see, melt can have no outputs, not mint.