`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.
txNew.vout.push_back(txout);
                }
                
                bool bnb_used;
                if (pick_new_inputs) {
                    nValueIn = 0;
                    setCoins.clear();
                    coin_selection_params.change_spend_size = CalculateMaximumSignedInputSize(change_prototype_txout, this);
                    coin_selection_params.effective_fee = nFeeRateNeeded;
                    if (!SelectCoins(vAvailableCoins, nValueToSelect, setCoins, nValueIn, coin_control, coin_selection_params, bnb_used))
                    {
                        
                        if (bnb_used) {
                            coin_selection_params.use_bnb = false;
                            continue;
                        }
                        else {
                            strFailReason = _("Insufficient funds");
                            return false;
                        }
                    }
                } else {
                    bnb_used = false;
                }
                const CAmount nChange = nValueIn - nValueToSelect;
                if (nChange > 0)
                {
                    
                    CTxOut newTxOut(nChange, scriptChange);