`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.
if (request.fHelp || request.params.size() < 1 || request.params.size() > 1) {
        throw std::runtime_error(
            "settxfee amount\n"
            "\nSet the transaction fee per kB for this wallet. Overrides the global -paytxfee command line parameter.\n"
            "\nArguments:\n"
            "1. amount         (numeric or string, required) The transaction fee in " + CURRENCY_UNIT + "/kB\n"
            "\nResult\n"
            "true|false        (boolean) Returns true if successful\n"
            "\nExamples:\n"
            + HelpExampleCli("settxfee", "0.00001")
            + HelpExampleRpc("settxfee", "0.00001")
        );
    }
    auto locked_chain = pwallet->chain().lock();
    LOCK(pwallet->cs_wallet);
    CAmount nAmount = AmountFromValue(request.params[0]);
    CFeeRate tx_fee_rate(nAmount, 1000);
    if (tx_fee_rate == 0) {
        
    } else if (tx_fee_rate < ::minRelayTxFee) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("txfee cannot be less than min relay tx fee (%s)", ::minRelayTxFee.ToString()));
    } else if (tx_fee_rate < pwallet->m_min_fee) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("txfee cannot be less than wallet min fee (%s)", pwallet->m_min_fee.ToString()));
    }
    pwallet->m_pay_tx_fee = tx_fee_rate;
    return true;
}
static UniValue getwalletinfo(const JSONRPCRequest& request)
{
    std::shared_ptr<CWallet> const wallet = GetWalletForJSONRPCRequest(request);