`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.
{
    std::map<CTxDestination, CAmount> balances;
    {
        LOCK(cs_wallet);
        for (const auto& walletEntry : mapWallet)
        {
            const CWalletTx *pcoin = &walletEntry.second;
            if (!pcoin->IsTrusted(locked_chain))
                continue;
            if (pcoin->IsImmatureCoinBase(locked_chain))
                continue;
            int nDepth = pcoin->GetDepthInMainChain(locked_chain);
            if (nDepth < (pcoin->IsFromMe(ISMINE_ALL) ? 0 : 1))
                continue;
            for (unsigned int i = 0; i < pcoin->tx->vout.size(); i++)
            {
                CTxDestination addr;
                if (!IsMine(pcoin->tx->vout[i]))
                    continue;
                if(!ExtractDestination(pcoin->tx->vout[i].scriptPubKey, addr))
                    continue;
                CAmount n = IsSpent(locked_chain, walletEntry.first, i) ? 0 : pcoin->tx->vout[i].nValue;
                if (!balances.count(addr))
                    balances[addr] = 0;