`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 (destinations.size() && (!fValidAddress || !destinations.count(address)))
            continue;
        UniValue entry(UniValue::VOBJ);
        entry.pushKV("txid", out.tx->GetHash().GetHex());
        entry.pushKV("vout", out.i);
        if (fValidAddress) {
            entry.pushKV("address", EncodeDestination(address));
            auto i = pwallet->mapAddressBook.find(address);
            if (i != pwallet->mapAddressBook.end()) {
                entry.pushKV("label", i->second.name);
            }
            if (scriptPubKey.IsPayToScriptHash()) {
                const CScriptID& hash = boost::get<CScriptID>(address);
                CScript redeemScript;
                if (pwallet->GetCScript(hash, redeemScript)) {
                    entry.pushKV("redeemScript", HexStr(redeemScript.begin(), redeemScript.end()));
                }
            }
        }
        entry.pushKV("scriptPubKey", HexStr(scriptPubKey.begin(), scriptPubKey.end()));
        entry.pushKV("amount", ValueFromAmount(out.tx->tx->vout[out.i].nValue));
        entry.pushKV("confirmations", out.nDepth);
        entry.pushKV("spendable", out.fSpendable);
        entry.pushKV("solvable", out.fSolvable);
        entry.pushKV("safe", out.fSafe);
        results.push_back(entry);
    }
    return results;
}
void FundTransaction(CWallet* const pwallet, CMutableTransaction& tx, CAmount& fee_out, int& change_position, UniValue options)