`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.
"  \"details\" : [\n"
            "    {\n"
            "      \"address\" : \"address\",          (string) The bitcoin address involved in the transaction\n"
            "      \"category\" : \"send|receive\",    (string) The category, either 'send' or 'receive'\n"
            "      \"amount\" : x.xxx,                 (numeric) The amount in " + CURRENCY_UNIT + "\n"
            "      \"label\" : \"label\",              (string) A comment for the address/transaction, if any\n"
            "      \"vout\" : n,                       (numeric) the vout value\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"
            "      \"abandoned\": xxx                  (bool) 'true' if the transaction has been abandoned (inputs are respendable). Only available for the \n"
            "                                           'send' category of transactions.\n"
            "    }\n"
            "    ,...\n"
            "  ],\n"
            "  \"hex\" : \"data\"         (string) Raw data for transaction\n"
            "}\n"
            "\nExamples:\n"
            + HelpExampleCli("gettransaction", "\"1075db55d416d3ca199f55b6084e2115b9345e16c5cf302fc80e9d5fbf5d48d\"")
            + HelpExampleCli("gettransaction", "\"1075db55d416d3ca199f55b6084e2115b9345e16c5cf302fc80e9d5fbf5d48d\" true")
            + HelpExampleRpc("gettransaction", "\"1075db55d416d3ca199f55b6084e2115b9345e16c5cf302fc80e9d5fbf5d48d\"")
        );
    
    
    pwallet->BlockUntilSyncedToCurrentChain();
    auto locked_chain = pwallet->chain().lock();
    LOCK(pwallet->cs_wallet);
    uint256 hash(ParseHashV(request.params[0], "txid"));
    isminefilter filter = ISMINE_SPENDABLE;
    if(!request.params[1].isNull())
        if(request.params[1].get_bool())