`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.
{
    AssertLockHeld(cs_wallet); 
    
    int nIn = 0;
    for (auto& input : tx.vin) {
        std::map<uint256, CWalletTx>::const_iterator mi = mapWallet.find(input.prevout.hash);
        if(mi == mapWallet.end() || input.prevout.n >= mi->second.tx->vout.size()) {
            return false;
        }
        const CScript& scriptPubKey = mi->second.tx->vout[input.prevout.n].scriptPubKey;
        const CAmount& amount = mi->second.tx->vout[input.prevout.n].nValue;
        SignatureData sigdata;
        if (!ProduceSignature(*this, MutableTransactionSignatureCreator(&tx, nIn, amount, SIGHASH_ALL), scriptPubKey, sigdata)) {
            return false;
        }
        UpdateInput(input, sigdata);
        nIn++;
    }
    return true;
}
bool CWallet::FundTransaction(CMutableTransaction& tx, CAmount& nFeeRet, int& nChangePosInOut, std::string& strFailReason, bool lockUnspents, const std::set<int>& setSubtractFeeFromOutputs, CCoinControl coinControl)