I'm sometimes getting an invalid json reply from `getwalletinfo` when rescanning is in progress.

The invalid part is this: `"scanning":{"duration":19,"progress":}}` (no value for `progress`).

I can't reliably reproduce this, but I did manage to run into this 3 times now (once every 10-20 attempts or so).

I'm running v0.20.0 and testing against a regtest instance. This happens while doing a batched `importmulti` of 2000 addresses (none of which have history).
int submitted_tx_count = 0;
    { 
        LOCK(cs_wallet);
        
        for (std::pair<const uint256, CWalletTx>& item : mapWallet) {
            CWalletTx& wtx = item.second;
            
            
            
            if (wtx.nTimeReceived > m_best_block_time - 5 * 60) continue;
            std::string unused_err_string;
            if (wtx.SubmitMemoryPoolAndRelay(unused_err_string, true)) ++submitted_tx_count;
        }
    } 
    if (submitted_tx_count > 0) {
        WalletLogPrintf("%s: resubmit %u unconfirmed transactions\n", __func__, submitted_tx_count);
    }
}
 
void MaybeResendWalletTxs()
{
    for (const std::shared_ptr<CWallet>& pwallet : GetWallets()) {
        pwallet->ResendWalletTransactions();
    }
}
/** @defgroup Actions
 *
 * @{
 */
CWallet::Balance CWallet::GetBalance(const int min_depth, bool avoid_reuse) const