`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.
{
    assert(!IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS));
    CKey key;
    key.MakeNewKey(true);
    return DeriveNewSeed(key);
}
CPubKey CWallet::DeriveNewSeed(const CKey& key)
{
    int64_t nCreationTime = GetTime();
    CKeyMetadata metadata(nCreationTime);
    
    CPubKey seed = key.GetPubKey();
    assert(key.VerifyPubKey(seed));
    
    metadata.hdKeypath     = "s";
    metadata.hd_seed_id = seed.GetID();
    {
        LOCK(cs_wallet);
        
        mapKeyMetadata[seed.GetID()] = metadata;
        
        if (!AddKeyPubKey(key, seed))
            throw std::runtime_error(std::string(__func__) + ": AddKeyPubKey failed");
    }
    return seed;
}
void CWallet::SetHDSeed(const CPubKey& seed)