bolt12: Add test vector for missing offer_amount with offer_currency #1279
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During differential fuzzing between C-lightning and rust-lightning, discovered that C-lightning incorrectly accepts offers with offer_currency set but offer_amount missing, while rust-lightning rejects them.
The BOLT 12 specification states in "Requirements For Offers":
This pr adds a test vector for the invalid offer:
lno1qcp4256ypgx9getnwss8vetrw3hhyuckyypwa3eyt44h6txtxquqh7lz5djge4afgfjn7k4rgrkuag0jsd5xvxgWhich contains CURRENCY=USD but no amount field, and should be rejected by all compliant implementations.
I got this test vector from:
https://github.com/ElementsProject/lightning/blob/c3362b057c2174589024254f4cab9eb8d955a26f/common/test/run-bolt12-encode-test.c#L439