`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.
{
    if (IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
        return false;
    }
    CKeyPool keypool;
    {
        LOCK(cs_wallet);
        int64_t nIndex;
        if (!ReserveKeyFromKeyPool(nIndex, keypool, internal)) {
            if (IsLocked()) return false;
            WalletBatch batch(*database);
            result = GenerateNewKey(batch, internal);
            return true;
        }
        KeepKey(nIndex);
        result = keypool.vchPubKey;
    }
    return true;
}
static int64_t GetOldestKeyTimeInPool(const std::set<int64_t>& setKeyPool, WalletBatch& batch) {