`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.
"      \"maximumAmount\"    (numeric or string, default=unlimited) Maximum value of each UTXO in " + CURRENCY_UNIT + "\n"
            "      \"maximumCount\"     (numeric or string, default=unlimited) Maximum number of UTXOs\n"
            "      \"minimumSumAmount\" (numeric or string, default=unlimited) Minimum sum value of all UTXOs in " + CURRENCY_UNIT + "\n"
            "    }\n"
            "\nResult\n"
            "[                   (array of json object)\n"
            "  {\n"
            "    \"txid\" : \"txid\",          (string) the transaction id \n"
            "    \"vout\" : n,               (numeric) the vout value\n"
            "    \"address\" : \"address\",    (string) the bitcoin address\n"
            "    \"label\" : \"label\",        (string) The associated label, or \"\" for the default label\n"
            "    \"scriptPubKey\" : \"key\",   (string) the script key\n"
            "    \"amount\" : x.xxx,         (numeric) the transaction output amount in " + CURRENCY_UNIT + "\n"
            "    \"confirmations\" : n,      (numeric) The number of confirmations\n"
            "    \"redeemScript\" : n        (string) The redeemScript if scriptPubKey is P2SH\n"
            "    \"spendable\" : xxx,        (bool) Whether we have the private keys to spend this output\n"
            "    \"solvable\" : xxx,         (bool) Whether we know how to spend this output, ignoring the lack of keys\n"
            "    \"safe\" : xxx              (bool) Whether this output is considered safe to spend. Unconfirmed transactions\n"
            "                              from outside keys and unconfirmed replacement transactions are considered unsafe\n"
            "                              and are not eligible for spending by fundrawtransaction and sendtoaddress.\n"
            "  }\n"
            "  ,...\n"
            "]\n"
            "\nExamples\n"
            + HelpExampleCli("listunspent", "")
            + HelpExampleCli("listunspent", "6 9999999 \"[\\\"1PGFqEzfmQch1gKD3ra4k18PNj3tTUUSqg\\\",\\\"1LtvqCaApEdUGFkpKMM4MstjcaL4dKg8SP\\\"]\"")
            + HelpExampleRpc("listunspent", "6, 9999999 \"[\\\"1PGFqEzfmQch1gKD3ra4k18PNj3tTUUSqg\\\",\\\"1LtvqCaApEdUGFkpKMM4MstjcaL4dKg8SP\\\"]\"")
            + HelpExampleCli("listunspent", "6 9999999 '[]' true '{ \"minimumAmount\": 0.005 }'")
            + HelpExampleRpc("listunspent", "6, 9999999, [] , true, { \"minimumAmount\": 0.005 } ")
        );