### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current behaviour

I randomly encountered this by loading a wallet created from master with an older version. I could trace it down to bd13dc2f46ea10302a928fcf0f53b7aed77ad260 (#26076), but I don't know descriptor wallets enough to understand what's going on (cc @Sjors @achow101).

### Expected behaviour

`bitcoind` starts, or at least tells me to use a later version if #26076 was a breaking change instead of corrupting `wallet.dat`.

### Steps to reproduce

(master, clean chain): 
`createwallet -regtest ""`
(v25.0rc2):
first `bitcoind -regtest` succeeds
then stop and restart the node: The second `bitcoind -regtest` leads to an InitError:
`Error: Error: Unable to expand wallet descriptor from cache`
now, the wallet cannot be loaded by either version.

### Relevant log output

_No response_

### How did you obtain Bitcoin Core

Compiled from source

### What version of Bitcoin Core are you using?

v25.0rc2 / master

### Operating system and version

Ubuntu

### Machine specifications

_No response_
desc_res.m_records, num_keys, num_ckeys, num_keys + num_ckeys);
    }
    return desc_res.m_result;
}
static DBErrors LoadAddressBookRecords(CWallet* pwallet, DatabaseBatch& batch) EXCLUSIVE_LOCKS_REQUIRED(pwallet->cs_wallet)
{
    AssertLockHeld(pwallet->cs_wallet);
    DBErrors result = DBErrors::LOAD_OK;
    
    LoadResult name_res = LoadRecords(pwallet, batch, DBKeys::NAME,
        [] (CWallet* pwallet, DataStream& key, CDataStream& value, std::string& err) EXCLUSIVE_LOCKS_REQUIRED(pwallet->cs_wallet) {
        std::string strAddress;
        key >> strAddress;
        std::string label;
        value >> label;
        pwallet->m_address_book[DecodeDestination(strAddress)].SetLabel(label);
        return DBErrors::LOAD_OK;
    });
    result = std::max(result, name_res.m_result);
    
    LoadResult purpose_res = LoadRecords(pwallet, batch, DBKeys::PURPOSE,
        [] (CWallet* pwallet, DataStream& key, CDataStream& value, std::string& err) EXCLUSIVE_LOCKS_REQUIRED(pwallet->cs_wallet) {
        std::string strAddress;
        key >> strAddress;
        std::string purpose_str;
        value >> purpose_str;
        std::optional<AddressPurpose> purpose{PurposeFromString(purpose_str)};
        if (!purpose) {
            pwallet->WalletLogPrintf("Warning: nonstandard purpose string '%s' for address '%s'\n", purpose_str, strAddress);
        }