`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::shared_ptr<CWallet> const wallet = GetWalletForJSONRPCRequest(request);
    CWallet* const pwallet = wallet.get();
    if (!EnsureWalletIsAvailable(pwallet, request.fHelp)) {
        return NullUniValue;
    }
    if (request.fHelp || request.params.size() < 1 || request.params.size() > 2)
        throw std::runtime_error(
            "gettransaction \"txid\" ( include_watchonly )\n"
            "\nGet detailed information about in-wallet transaction <txid>\n"
            "\nArguments:\n"
            "1. \"txid\"                  (string, required) The transaction id\n"
            "2. \"include_watchonly\"     (bool, optional, default=false) Whether to include watch-only addresses in balance calculation and details[]\n"
            "\nResult:\n"
            "{\n"
            "  \"amount\" : x.xxx,        (numeric) The transaction amount in " + CURRENCY_UNIT + "\n"
            "  \"fee\": x.xxx,            (numeric) The amount of the fee in " + CURRENCY_UNIT + ". This is negative and only available for the \n"
            "                              'send' category of transactions.\n"
            "  \"confirmations\" : n,     (numeric) The number of confirmations\n"
            "  \"blockhash\" : \"hash\",  (string) The block hash\n"
            "  \"blockindex\" : xx,       (numeric) The index of the transaction in the block that includes it\n"
            "  \"blocktime\" : ttt,       (numeric) The time in seconds since epoch (1 Jan 1970 GMT)\n"
            "  \"txid\" : \"transactionid\",   (string) The transaction id.\n"
            "  \"time\" : ttt,            (numeric) The transaction time in seconds since epoch (1 Jan 1970 GMT)\n"
            "  \"timereceived\" : ttt,    (numeric) The time received in seconds since epoch (1 Jan 1970 GMT)\n"
            "  \"bip125-replaceable\": \"yes|no|unknown\",  (string) Whether this transaction could be replaced due to BIP125 (replace-by-fee);\n"
            "                                                   may be unknown for unconfirmed transactions not in the mempool\n"