### 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_
for (auto it = spks.begin(); it != spks.end();) {
        const CScript& spk = *it;
        
        uint64_t creation_time = 0;
        const auto& mit = m_script_metadata.find(CScriptID(spk));
        if (mit != m_script_metadata.end()) {
            creation_time = mit->second.nCreateTime;
        }
        
        std::unique_ptr<Descriptor> desc = InferDescriptor(spk, *GetSolvingProvider(spk));
        
        std::vector<CScript> scripts;
        FlatSigningProvider keys;
        if (!desc->Expand(0, DUMMY_SIGNING_PROVIDER, scripts, keys)) {
            assert(false);
        }
        std::set<CKeyID> privkeyids;
        for (const auto& key_orig_pair : keys.origins) {
            privkeyids.insert(key_orig_pair.first);
        }
        std::vector<CScript> desc_spks;
        
        std::string desc_str;
        bool watchonly = !desc->ToPrivateString(*this, desc_str);
        if (watchonly && !m_storage.IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
            out.watch_descs.push_back({desc->ToString(), creation_time});
            
            FlatSigningProvider provider;
            desc->Expand(0, provider, desc_spks, provider);
        } else {