Introduce the `fixFillOrKill` amendment.
Fix an edge case occurring when an offer with `tfFillOrKill` set (but
without `tfSell` set) fails to cross an offer with a better rate. If
`tfFillOrKill` is set, then the owner must receive the full TakerPays.
Without this amendment, an offer fails if the entire `TakerGets` is not
spent. With this amendment, when `tfSell` is not set, the entire
`TakerGets` does not have to be spent.
For details about OfferCreate, see: https://xrpl.org/offercreate.htmlFix#4684
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Co-authored-by: Scott Schurr <scott@ripple.com>
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