`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)
        throw std::runtime_error(
            "loadwallet \"filename\"\n"
            "\nLoads a wallet from a wallet file or directory."
            "\nNote that all wallet command-line options used when starting bitcoind will be"
            "\napplied to the new wallet (eg -zapwallettxes, upgradewallet, rescan, etc).\n"
            "\nArguments:\n"
            "1. \"filename\"    (string, required) The wallet directory or .dat file.\n"
            "\nResult:\n"
            "{\n"
            "  \"name\" :    <wallet_name>,        (string) The wallet name if loaded successfully.\n"
            "  \"warning\" : <warning>,            (string) Warning message if wallet was not loaded cleanly.\n"
            "}\n"
            "\nExamples:\n"