If a tx is marked as failed (because it never shows up in the
daemon's pool), its key images get reset back to unspent so they
can be used in future txs.
If the tx re-enters the daemon's pool (e.g. it's removed from the
pool and then relayed back), then the wallet incorrectly maintains
that the tx's key images are unspent.
This change ensures the wallet re-marks the tx's key images as
spent if the tx re-appears in the node's pool.
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