For legacy payments, the HTLC Hash field may be nil in the bbolt
backend. Previously, the migration would fail with "HTLC attempt X
missing payment hash" when encountering such payments.
This commit fixes the migration by falling back to the parent payment
hash when the HTLC-specific hash is nil. This is consistent with how
the router handles legacy payments (see patchLegacyPaymentHash in
payment_lifecycle.go).
The validation logic is also updated to apply the same fallback when
comparing bbolt data with migrated SQL data, ensuring the comparison
succeeds.
ziggie
89685de16e