### 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_
{
    if (n_signed) {
        *n_signed = 0;
    }
    for (unsigned int i = 0; i < psbtx.tx->vin.size(); ++i) {
        const CTxIn& txin = psbtx.tx->vin[i];
        PSBTInput& input = psbtx.inputs.at(i);
        if (PSBTInputSigned(input)) {
            continue;
        }
        
        if (sign && input.sighash_type != std::nullopt && *input.sighash_type != sighash_type) {
            return TransactionError::SIGHASH_MISMATCH;
        }
        
        CScript script;
        if (!input.witness_utxo.IsNull()) {
            script = input.witness_utxo.scriptPubKey;
        } else if (input.non_witness_utxo) {
            if (txin.prevout.n >= input.non_witness_utxo->vout.size()) {
                return TransactionError::MISSING_INPUTS;
            }
            script = input.non_witness_utxo->vout[txin.prevout.n].scriptPubKey;
        } else {
            
            continue;
        }