### 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_
{
    LOCK(cs_desc_man);
    std::vector<WalletDestination> result;
    if (IsMine(script)) {
        int32_t index = m_map_script_pub_keys[script];
        if (index >= m_wallet_descriptor.next_index) {
            WalletLogPrintf("%s: Detected a used keypool item at index %d, mark all keypool items up to this item as used\n", __func__, index);
            auto out_keys = std::make_unique<FlatSigningProvider>();
            std::vector<CScript> scripts_temp;
            while (index >= m_wallet_descriptor.next_index) {
                if (!m_wallet_descriptor.descriptor->ExpandFromCache(m_wallet_descriptor.next_index, m_wallet_descriptor.cache, scripts_temp, *out_keys)) {
                    throw std::runtime_error(std::string(__func__) + ": Unable to expand descriptor from cache");
                }
                CTxDestination dest;
                ExtractDestination(scripts_temp[0], dest);
                result.push_back({dest, std::nullopt});
                m_wallet_descriptor.next_index++;
            }
        }
        if (!TopUp()) {
            WalletLogPrintf("%s: Topping up keypool failed (locked wallet)\n", __func__);
        }
    }
    return result;
}
void DescriptorScriptPubKeyMan::AddDescriptorKey(const CKey& key, const CPubKey &pubkey)