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).
break;
            }
            
            block_hash = next_block_hash;
            ++block_height;
            progress_current = chain().guessVerificationProgress(block_hash);
            
            const uint256 prev_tip_hash = tip_hash;
            tip_hash = WITH_LOCK(cs_wallet, return GetLastBlockHash());
            if (!max_height && prev_tip_hash != tip_hash) {
                
                progress_end = chain().guessVerificationProgress(tip_hash);
            }
        }
    }
    ShowProgress(strprintf("%s " + _("Rescanning...").translated, GetDisplayName()), 100); 
    if (block_height && fAbortRescan) {
        WalletLogPrintf("Rescan aborted at block %d. Progress=%f\n", block_height, progress_current);
        result.status = ScanResult::USER_ABORT;
    } else if (block_height && chain().shutdownRequested()) {
        WalletLogPrintf("Rescan interrupted by shutdown request at block %d. Progress=%f\n", block_height, progress_current);
        result.status = ScanResult::USER_ABORT;
    } else {
        WalletLogPrintf("Rescan completed in %15dms\n", GetTimeMillis() - start_time);
    }
    return result;
}
void CWallet::ReacceptWalletTransactions()