`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 (request.fHelp || request.params.size() != 0) {
        throw std::runtime_error(
            "listwalletdir\n"
            "Returns a list of wallets in the wallet directory.\n"
            "{\n"
            "  \"wallets\" : [                (json array of objects)\n"
            "    {\n"
            "      \"name\" : \"name\"          (string) The wallet name\n"
            "    }\n"
            "    ,...\n"
            "  ]\n"
            "}\n"
            "\nExamples:\n"
            + HelpExampleCli("listwalletdir", "")
            + HelpExampleRpc("listwalletdir", "")
        );
    }
    UniValue wallets(UniValue::VARR);
    for (const auto& path : ListWalletDir()) {
        UniValue wallet(UniValue::VOBJ);
        wallet.pushKV("name", path.string());
        wallets.push_back(wallet);
    }
    UniValue result(UniValue::VOBJ);
    result.pushKV("wallets", wallets);
    return result;
}
static UniValue listwallets(const JSONRPCRequest& request)