### 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_KeyStore);
    
    bool keypool_has_keys;
    if (internal && m_storage.CanSupportFeature(FEATURE_HD_SPLIT)) {
        keypool_has_keys = setInternalKeyPool.size() > 0;
    } else {
        keypool_has_keys = KeypoolCountExternalKeys() > 0;
    }
    
    if (!keypool_has_keys) {
        return CanGenerateKeys();
    }
    return keypool_has_keys;
}
bool LegacyScriptPubKeyMan::Upgrade(int prev_version, int new_version, bilingual_str& error)
{
    LOCK(cs_KeyStore);
    if (m_storage.IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
        
        return true;
    }
    bool hd_upgrade = false;
    bool split_upgrade = false;
    if (IsFeatureSupported(new_version, FEATURE_HD) && !IsHDEnabled()) {
        WalletLogPrintf("Upgrading wallet to HD\n");
        m_storage.SetMinVersion(FEATURE_HD);
        
        CPubKey masterPubKey = GenerateNewSeed();