### 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_
error = strprintf("tr(): %s", error);
            return nullptr;
        }
        ++key_exp_index;
        std::vector<std::unique_ptr<DescriptorImpl>> subscripts; 
        std::vector<int> depths; 
        if (expr.size()) {
            if (!Const(",", expr)) {
                error = strprintf("tr: expected ',', got '%c'", expr[0]);
                return nullptr;
            }
            /** The path from the top of the tree to what we're currently processing.
             * branches[i] == false: left branch in the i'th step from the top; true: right branch.
             */
            std::vector<bool> branches;
            
            
            do {
                
                while (Const("{", expr)) {
                    branches.push_back(false); 
                    if (branches.size() > TAPROOT_CONTROL_MAX_NODE_COUNT) {
                        error = strprintf("tr() supports at most %i nesting levels", TAPROOT_CONTROL_MAX_NODE_COUNT);
                        return nullptr;
                    }
                }
                
                auto sarg = Expr(expr);
                subscripts.emplace_back(ParseScript(key_exp_index, sarg, ParseScriptContext::P2TR, out, error));
                if (!subscripts.back()) return nullptr;