`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(
            "bumpfee \"txid\" ( options ) \n"
            "\nBumps the fee of an opt-in-RBF transaction T, replacing it with a new transaction B.\n"
            "An opt-in RBF transaction with the given txid must be in the wallet.\n"
            "The command will pay the additional fee by decreasing (or perhaps removing) its change output.\n"
            "If the change output is not big enough to cover the increased fee, the command will currently fail\n"
            "instead of adding new inputs to compensate. (A future implementation could improve this.)\n"
            "The command will fail if the wallet or mempool contains a transaction that spends one of T's outputs.\n"
            "By default, the new fee will be calculated automatically using estimatesmartfee.\n"
            "The user can specify a confirmation target for estimatesmartfee.\n"
            "Alternatively, the user can specify totalFee, or use RPC settxfee to set a higher fee rate.\n"
            "At a minimum, the new fee rate must be high enough to pay an additional new relay fee (incrementalfee\n"
            "returned by getnetworkinfo) to enter the node's mempool.\n"
            "\nArguments:\n"
            "1. txid                  (string, required) The txid to be bumped\n"
            "2. options               (object, optional)\n"
            "   {\n"
            "     \"confTarget\"        (numeric, optional) Confirmation target (in blocks)\n"
            "     \"totalFee\"          (numeric, optional) Total fee (NOT feerate) to pay, in satoshis.\n"
            "                         In rare cases, the actual fee paid might be slightly higher than the specified\n"
            "                         totalFee if the tx change output has to be removed because it is too close to\n"
            "                         the dust threshold.\n"
            "     \"replaceable\"       (boolean, optional, default true) Whether the new transaction should still be\n"
            "                         marked bip-125 replaceable. If true, the sequence numbers in the transaction will\n"