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).
#include <wallet/wallet.h>
#include <chain.h>
#include <consensus/consensus.h>
#include <consensus/validation.h>
#include <fs.h>
#include <interfaces/chain.h>
#include <interfaces/wallet.h>
#include <key.h>
#include <key_io.h>
#include <optional.h>
#include <policy/fees.h>
#include <policy/policy.h>
#include <primitives/block.h>
#include <primitives/transaction.h>
#include <script/descriptor.h>
#include <script/script.h>
#include <script/signingprovider.h>
#include <txmempool.h>
#include <util/bip32.h>
#include <util/check.h>
#include <util/error.h>
#include <util/fees.h>
#include <util/moneystr.h>
#include <util/rbf.h>
#include <util/string.h>