### 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);
    if (m_storage.IsLocked()) {
        return std::nullopt;
    }
    MigrationData out;
    std::unordered_set<CScript, SaltedSipHasher> spks{GetScriptPubKeys()};
    
    std::set<CKeyID> keyids;
    for (const auto& key_pair : mapKeys) {
        keyids.insert(key_pair.first);
    }
    for (const auto& key_pair : mapCryptedKeys) {
        keyids.insert(key_pair.first);
    }
    
    
    for (auto keyid_it = keyids.begin(); keyid_it != keyids.end();) {
        const CKeyID& keyid = *keyid_it;
        const auto& it = mapKeyMetadata.find(keyid);
        if (it != mapKeyMetadata.end()) {
            const CKeyMetadata& meta = it->second;
            if (meta.hdKeypath == "s" || meta.hdKeypath == "m") {
                keyid_it++;
                continue;
            }
            if (m_hd_chain.seed_id == meta.hd_seed_id || m_inactive_hd_chains.count(meta.hd_seed_id) > 0) {
                keyid_it = keyids.erase(keyid_it);
                continue;