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).
LOCK(cs_wallet);
    SyncTransaction(tx, {CWalletTx::Status::UNCONFIRMED,  0,  {},  0});
    auto it = mapWallet.find(tx->GetHash());
    if (it != mapWallet.end()) {
        it->second.fInMempool = true;
    }
}
void CWallet::transactionRemovedFromMempool(const CTransactionRef& tx, MemPoolRemovalReason reason, uint64_t mempool_sequence) {
    LOCK(cs_wallet);
    auto it = mapWallet.find(tx->GetHash());
    if (it != mapWallet.end()) {
        it->second.fInMempool = false;
    }
    
    
    if (reason == MemPoolRemovalReason::CONFLICT) {