`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.
"4. address_filter    (string, optional) If present, only return information on this address.\n"
            "\nResult:\n"
            "[\n"
            "  {\n"
            "    \"involvesWatchonly\" : true,        (bool) Only returned if imported addresses were involved in transaction\n"
            "    \"address\" : \"receivingaddress\",  (string) The receiving address\n"
            "    \"amount\" : x.xxx,                  (numeric) The total amount in " + CURRENCY_UNIT + " received by the address\n"
            "    \"confirmations\" : n,               (numeric) The number of confirmations of the most recent transaction included\n"
            "    \"label\" : \"label\",               (string) The label of the receiving address. The default label is \"\".\n"
            "    \"txids\": [\n"
            "       \"txid\",                         (string) The ids of transactions received with the address \n"
            "       ...\n"
            "    ]\n"
            "  }\n"
            "  ,...\n"
            "]\n"
            "\nExamples:\n"
            + HelpExampleCli("listreceivedbyaddress", "")
            + HelpExampleCli("listreceivedbyaddress", "6 true")
            + HelpExampleRpc("listreceivedbyaddress", "6, true, true")
            + HelpExampleRpc("listreceivedbyaddress", "6, true, true, \"1M72Sfpbz1BPpXFHz9m3CdqATR44Jvaydd\"")
        );
    
    
    pwallet->BlockUntilSyncedToCurrentChain();
    auto locked_chain = pwallet->chain().lock();
    LOCK(pwallet->cs_wallet);
    return ListReceived(*locked_chain, pwallet, request.params, false);
}
static UniValue listreceivedbylabel(const JSONRPCRequest& request)