`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.
walletInstance->WalletLogPrintf("Upgrading wallet to HD\n");
            walletInstance->SetMinVersion(FEATURE_HD);
            
            CPubKey masterPubKey = walletInstance->GenerateNewSeed();
            walletInstance->SetHDSeed(masterPubKey);
            hd_upgrade = true;
        }
        
        if (walletInstance->CanSupportFeature(FEATURE_HD_SPLIT)) {
            walletInstance->WalletLogPrintf("Upgrading wallet to use HD chain split\n");
            walletInstance->SetMinVersion(FEATURE_PRE_SPLIT_KEYPOOL);
            split_upgrade = FEATURE_HD_SPLIT > prev_version;
        }
        
        if (split_upgrade) {
            walletInstance->MarkPreSplitKeys();
        }
        
        if (hd_upgrade) {
            if (!walletInstance->TopUpKeyPool()) {
                InitError(_("Unable to generate keys"));
                return nullptr;
            }
        }
    }
    if (fFirstRun)
    {
        
        walletInstance->SetMinVersion(FEATURE_LATEST);
        if ((wallet_creation_flags & WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {