`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.
wallet->AddKeyPubKey(coinbaseKey, coinbaseKey.GetPubKey());
        JSONRPCRequest request;
        request.params.setArray();
        request.params.push_back(backup_file);
        AddWallet(wallet);
        ::dumpwallet(request);
        RemoveWallet(wallet);
    }
    
    
    {
        std::shared_ptr<CWallet> wallet = std::make_shared<CWallet>(*chain, WalletLocation(), WalletDatabase::CreateDummy());
        JSONRPCRequest request;
        request.params.setArray();
        request.params.push_back(backup_file);
        AddWallet(wallet);
        ::importwallet(request);
        RemoveWallet(wallet);
        LOCK(wallet->cs_wallet);
        BOOST_CHECK_EQUAL(wallet->mapWallet.size(), 3U);
        BOOST_CHECK_EQUAL(m_coinbase_txns.size(), 103U);
        for (size_t i = 0; i < m_coinbase_txns.size(); ++i) {
            bool found = wallet->GetWalletTx(m_coinbase_txns[i]->GetHash());
            bool expected = i >= 100;
            BOOST_CHECK_EQUAL(found, expected);
        }
    }
    SetMockTime(0);
}
BOOST_FIXTURE_TEST_CASE(coin_mark_dirty_immature_credit, TestChain100Setup)