### 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_
{
    AssertLockHeld(cs_desc_man);
    assert(!m_storage.IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS));
    
    if (m_map_keys.find(pubkey.GetID()) != m_map_keys.end() ||
        m_map_crypted_keys.find(pubkey.GetID()) != m_map_crypted_keys.end()) {
        return true;
    }
    if (m_storage.HasEncryptionKeys()) {
        if (m_storage.IsLocked()) {
            return false;
        }
        std::vector<unsigned char> crypted_secret;
        CKeyingMaterial secret(key.begin(), key.end());
        if (!EncryptSecret(m_storage.GetEncryptionKey(), secret, pubkey.GetHash(), crypted_secret)) {
            return false;
        }
        m_map_crypted_keys[pubkey.GetID()] = make_pair(pubkey, crypted_secret);
        return batch.WriteCryptedDescriptorKey(GetID(), pubkey, crypted_secret);
    } else {
        m_map_keys[pubkey.GetID()] = key;
        return batch.WriteDescriptorKey(GetID(), pubkey, key.GetPrivKey());
    }
}
bool DescriptorScriptPubKeyMan::SetupDescriptorGeneration(const CExtKey& master_key, OutputType addr_type, bool internal)
{
    LOCK(cs_desc_man);
    assert(m_storage.IsWalletFlagSet(WALLET_FLAG_DESCRIPTORS));
    
    if (m_wallet_descriptor.descriptor) {