`ScanForWalletTransactions()` has the following comment about its return value:

```
 * Returns null if scan was successful. Otherwise, if a complete rescan was not
 * possible (due to pruning or corruption), returns pointer to the most recent
 * block that could not be scanned.
```

This is not strictly true. If `abortrescan` is called, then `ScanForWalletTransactions()` will return `nullptr`, even though the scan wasn't successful to the tip.

This in turn causes a minor bug in `importmulti`, where the call doesn't return the correct error and warning about potentially not finding transactions if `abortrescan` was called.

I think the correct fix is for `ScanForWalletTransactions()` to inform the caller that the rescan was aborted.
bool isAbandoned() const { return (hashBlock == ABANDON_HASH); }
    void setAbandoned() { hashBlock = ABANDON_HASH; }
    const uint256& GetHash() const { return tx->GetHash(); }
    bool IsCoinBase() const { return tx->IsCoinBase(); }
    bool IsImmatureCoinBase(interfaces::Chain::Lock& locked_chain) const;
};
int CalculateMaximumSignedInputSize(const CTxOut& txout, const CWallet* pwallet, bool use_max_sig = false);
/**
 * A transaction with a bunch of additional info that only the owner cares about.
 * It includes any unrecorded transactions needed to link it back to the block chain.
 */
class CWalletTx : public CMerkleTx
{
private:
    const CWallet* pwallet;
public:
    /**
     * Key/value map with information about the transaction.
     *
     * The following keys can be read and written through the map and are
     * serialized in the wallet database:
     *
     *     "comment", "to"   - comment strings provided to sendtoaddress,
     *                         and sendmany wallet RPCs
     *     "replaces_txid"   - txid (as HexStr) of transaction replaced by
     *                         bumpfee on transaction created by bumpfee
     *     "replaced_by_txid" - txid (as HexStr) of transaction created by
     *                         bumpfee on transaction replaced by bumpfee