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).
{
    
    if (!fBroadcastTransactions)
        return;
    std::map<int64_t, CWalletTx*> mapSorted;
    
    for (std::pair<const uint256, CWalletTx>& item : mapWallet) {
        const uint256& wtxid = item.first;
        CWalletTx& wtx = item.second;
        assert(wtx.GetHash() == wtxid);
        int nDepth = wtx.GetDepthInMainChain();
        if (!wtx.IsCoinBase() && (nDepth == 0 && !wtx.isAbandoned())) {
            mapSorted.insert(std::make_pair(wtx.nOrderPos, &wtx));
        }
    }
    
    for (const std::pair<const int64_t, CWalletTx*>& item : mapSorted) {
        CWalletTx& wtx = *(item.second);
        std::string unused_err_string;
        wtx.SubmitMemoryPoolAndRelay(unused_err_string, false);
    }
}
bool CWalletTx::SubmitMemoryPoolAndRelay(std::string& err_string, bool relay)