`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;
    }
    {
        LOCK(cs_wallet);
        WalletBatch batch(*database);
        for (const int64_t nIndex : setInternalKeyPool) {
            batch.ErasePool(nIndex);
        }
        setInternalKeyPool.clear();
        for (const int64_t nIndex : setExternalKeyPool) {
            batch.ErasePool(nIndex);
        }
        setExternalKeyPool.clear();
        for (const int64_t nIndex : set_pre_split_keypool) {
            batch.ErasePool(nIndex);
        }
        set_pre_split_keypool.clear();
        m_pool_key_to_index.clear();
        if (!TopUpKeyPool()) {
            return false;
        }
        WalletLogPrintf("CWallet::NewKeyPool rewrote keypool\n");
    }
    return true;
}
size_t CWallet::KeypoolCountExternalKeys()