### 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);
    WatchKeyMap::const_iterator it = mapWatchKeys.find(address);
    if (it != mapWatchKeys.end()) {
        pubkey_out = it->second;
        return true;
    }
    return false;
}
bool LegacyScriptPubKeyMan::GetPubKey(const CKeyID &address, CPubKey& vchPubKeyOut) const
{
    LOCK(cs_KeyStore);
    if (!m_storage.HasEncryptionKeys()) {
        if (!FillableSigningProvider::GetPubKey(address, vchPubKeyOut)) {
            return GetWatchPubKey(address, vchPubKeyOut);
        }
        return true;
    }
    CryptedKeyMap::const_iterator mi = mapCryptedKeys.find(address);
    if (mi != mapCryptedKeys.end())
    {
        vchPubKeyOut = (*mi).second.first;
        return true;
    }
    
    return GetWatchPubKey(address, vchPubKeyOut);
}
CPubKey LegacyScriptPubKeyMan::GenerateNewKey(WalletBatch &batch, CHDChain& hd_chain, bool internal)