`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() < 1 || request.params.size() > 2) {
        throw std::runtime_error(
            "createwallet \"wallet_name\" ( disable_private_keys )\n"
            "\nCreates and loads a new wallet.\n"
            "\nArguments:\n"
            "1. \"wallet_name\"          (string, required) The name for the new wallet. If this is a path, the wallet will be created at the path location.\n"
            "2. disable_private_keys   (boolean, optional, default: false) Disable the possibility of private keys (only watchonlys are possible in this mode).\n"
            "\nResult:\n"
            "{\n"
            "  \"name\" :    <wallet_name>,        (string) The wallet name if created successfully. If the wallet was created using a full path, the wallet_name will be the full path.\n"
            "  \"warning\" : <warning>,            (string) Warning message if wallet was not loaded cleanly.\n"
            "}\n"
            "\nExamples:\n"
            + HelpExampleCli("createwallet", "\"testwallet\"")
            + HelpExampleRpc("createwallet", "\"testwallet\"")
        );
    }
    std::string error;
    std::string warning;
    bool disable_privatekeys = false;
    if (!request.params[1].isNull()) {
        disable_privatekeys = request.params[1].get_bool();
    }
    WalletLocation location(request.params[0].get_str());
    if (location.Exists()) {