`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.
CAmount nAmount = AmountFromValue(request.params[1]);
    if (nAmount <= 0)
        throw JSONRPCError(RPC_TYPE_ERROR, "Invalid amount for send");
    
    mapValue_t mapValue;
    if (!request.params[2].isNull() && !request.params[2].get_str().empty())
        mapValue["comment"] = request.params[2].get_str();
    if (!request.params[3].isNull() && !request.params[3].get_str().empty())
        mapValue["to"] = request.params[3].get_str();
    bool fSubtractFeeFromAmount = false;
    if (!request.params[4].isNull()) {
        fSubtractFeeFromAmount = request.params[4].get_bool();
    }
    CCoinControl coin_control;
    if (!request.params[5].isNull()) {
        coin_control.m_signal_bip125_rbf = request.params[5].get_bool();
    }
    if (!request.params[6].isNull()) {
        coin_control.m_confirm_target = ParseConfirmTarget(request.params[6]);
    }
    if (!request.params[7].isNull()) {
        if (!FeeModeFromString(request.params[7].get_str(), coin_control.m_fee_mode)) {
            throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid estimate_mode parameter");
        }
    }
    EnsureWalletIsUnlocked(pwallet);
    CTransactionRef tx = SendMoney(*locked_chain, pwallet, dest, nAmount, fSubtractFeeFromAmount, coin_control, std::move(mapValue));
    return tx->GetHash().GetHex();
}
static UniValue listaddressgroupings(const JSONRPCRequest& request)