### 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_
#include <script/descriptor.h>
#include <hash.h>
#include <key_io.h>
#include <pubkey.h>
#include <script/miniscript.h>
#include <script/script.h>
#include <script/standard.h>
#include <uint256.h>
#include <common/args.h>
#include <span.h>
#include <util/bip32.h>
#include <util/spanparsing.h>
#include <util/strencodings.h>
#include <util/vector.h>
#include <memory>
#include <optional>
#include <string>
#include <vector>
namespace {
/*
 * Interprets c as 8 groups of 5 bits which are the coefficients of a degree 8 polynomial over GF(32),