Note that the slight code reorder changes the JSON order, which is generally
undefined, but our doc checker is very strict!
Changelog-Changed: `xpay` now gives the same JSON success return as documented by `pay` when `xpay-handle-pay` is set.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Fixes: https://github.com/ElementsProject/lightning/issues/7923