`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(!crypter.SetKeyFromPassphrase(strOldWalletPassphrase, pMasterKey.second.vchSalt, pMasterKey.second.nDeriveIterations, pMasterKey.second.nDerivationMethod))
                return false;
            if (!crypter.Decrypt(pMasterKey.second.vchCryptedKey, _vMasterKey))
                return false;
            if (CCryptoKeyStore::Unlock(_vMasterKey))
            {
                int64_t nStartTime = GetTimeMillis();
                crypter.SetKeyFromPassphrase(strNewWalletPassphrase, pMasterKey.second.vchSalt, pMasterKey.second.nDeriveIterations, pMasterKey.second.nDerivationMethod);
                pMasterKey.second.nDeriveIterations = static_cast<unsigned int>(pMasterKey.second.nDeriveIterations * (100 / ((double)(GetTimeMillis() - nStartTime))));
                nStartTime = GetTimeMillis();
                crypter.SetKeyFromPassphrase(strNewWalletPassphrase, pMasterKey.second.vchSalt, pMasterKey.second.nDeriveIterations, pMasterKey.second.nDerivationMethod);
                pMasterKey.second.nDeriveIterations = (pMasterKey.second.nDeriveIterations + static_cast<unsigned int>(pMasterKey.second.nDeriveIterations * 100 / ((double)(GetTimeMillis() - nStartTime)))) / 2;
                if (pMasterKey.second.nDeriveIterations < 25000)
                    pMasterKey.second.nDeriveIterations = 25000;
                WalletLogPrintf("Wallet passphrase changed to an nDeriveIterations of %i\n", pMasterKey.second.nDeriveIterations);
                if (!crypter.SetKeyFromPassphrase(strNewWalletPassphrase, pMasterKey.second.vchSalt, pMasterKey.second.nDeriveIterations, pMasterKey.second.nDerivationMethod))
                    return false;
                if (!crypter.Encrypt(_vMasterKey, pMasterKey.second.vchCryptedKey))
                    return false;
                WalletBatch(*database).WriteMasterKey(pMasterKey.first, pMasterKey.second);
                if (fWasLocked)
                    Lock();
                return true;
            }
        }
    }
    return false;
}
void CWallet::ChainStateFlushed(const CBlockLocator& loc)