`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 (!ret)
                {
                    strFailReason = _("Keypool ran out, please call keypoolrefill first");
                    return false;
                }
                const OutputType change_type = TransactionChangeType(coin_control.m_change_type ? *coin_control.m_change_type : m_default_change_type, vecSend);
                LearnRelatedScripts(vchPubKey, change_type);
                scriptChange = GetScriptForDestination(GetDestinationForKey(vchPubKey, change_type));
            }
            CTxOut change_prototype_txout(0, scriptChange);
            coin_selection_params.change_output_size = GetSerializeSize(change_prototype_txout);
            CFeeRate discard_rate = GetDiscardRate(*this, ::feeEstimator);
            
            CFeeRate nFeeRateNeeded = GetMinimumFeeRate(*this, coin_control, ::mempool, ::feeEstimator, &feeCalc);
            nFeeRet = 0;
            bool pick_new_inputs = true;
            CAmount nValueIn = 0;
            
            
            coin_selection_params.use_bnb = nSubtractFeeFromAmount == 0; 
            
            while (true)
            {
                nChangePosInOut = nChangePosRequest;
                txNew.vin.clear();
                txNew.vout.clear();
                bool fFirst = true;
                CAmount nValueToSelect = nValue;
                if (nSubtractFeeFromAmount == 0)
                    nValueToSelect += nFeeRet;