`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.
throw std::runtime_error(
            "walletpassphrase <passphrase> <timeout>\n"
            "Stores the wallet decryption key in memory for <timeout> seconds.");
    pwallet->TopUpKeyPool();
    pwallet->nRelockTime = GetTime() + nSleepTime;
    
    
    
    std::weak_ptr<CWallet> weak_wallet = wallet;
    RPCRunLater(strprintf("lockwallet(%s)", pwallet->GetName()), [weak_wallet] {
        if (auto shared_wallet = weak_wallet.lock()) {
            LOCK(shared_wallet->cs_wallet);
            shared_wallet->Lock();
            shared_wallet->nRelockTime = 0;
        }
    }, nSleepTime);
    return NullUniValue;
}
static UniValue walletpassphrasechange(const JSONRPCRequest& request)
{
    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() != 2) {
        throw std::runtime_error(
            "walletpassphrasechange \"oldpassphrase\" \"newpassphrase\"\n"
            "\nChanges the wallet passphrase from 'oldpassphrase' to 'newpassphrase'.\n"
            "\nArguments:\n"