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).
bool reorg = false;
        if (chain().findBlock(block_hash, FoundBlock().data(block)) && !block.IsNull()) {
            LOCK(cs_wallet);
            next_block = chain().findNextBlock(block_hash, block_height, FoundBlock().hash(next_block_hash), &reorg);
            if (reorg) {
                
                
                
                
                result.last_failed_block = block_hash;
                result.status = ScanResult::FAILURE;
                break;
            }
            for (size_t posInBlock = 0; posInBlock < block.vtx.size(); ++posInBlock) {
                SyncTransaction(block.vtx[posInBlock], {CWalletTx::Status::CONFIRMED, block_height, block_hash, (int)posInBlock}, fUpdate);
            }
            
            result.last_scanned_block = block_hash;
            result.last_scanned_height = block_height;
        } else {
            
            result.last_failed_block = block_hash;
            result.status = ScanResult::FAILURE;
            next_block = chain().findNextBlock(block_hash, block_height, FoundBlock().hash(next_block_hash), &reorg);
        }
        if (max_height && block_height >= *max_height) {
            break;
        }
        {
            if (!next_block || reorg) {