Attempting to load a wallet with an unknown descriptor causes a fatal error:

```
2022-09-06T01:51:06Z init message: Loading wallet…
2022-09-06T01:51:06Z [descriptor] Invalid descriptor: Can only have tr at top level: iostream error
2022-09-06T01:51:06Z [descriptor] Invalid descriptor: Can only have tr at top level: iostream error
2022-09-06T01:51:06Z [descriptor] Setting spkMan to active: id = 50e6032b4d1d62c020ebb6a4d0c8fafc6f01ea80f4d2a41c1a256086611636e9, type = legacy, internal = false
2022-09-06T01:51:06Z [descriptor] Setting spkMan to active: id = 7f709abbde61e8c253798375692bf41202e625ed74a65f9474d464be34fb2870, type = p2sh-segwit, internal = false
2022-09-06T01:51:06Z [descriptor] Setting spkMan to active: id = 2dc6c34099e0ca1235fc990a51042967ecbc8c8ac57062f964739cba2f451be8, type = bech32, internal = false
2022-09-06T01:51:06Z [descriptor] Setting spkMan to active: id = 8d3c63ea1ac9936e789713dc8bae857d328ff029ab9392e67c716752e9b11b0c, type = bech32m, internal = false
2022-09-06T01:51:06Z [descriptor] Releasing wallet
2022-09-06T01:51:06Z 

************************
EXCEPTION: St12out_of_range       
map::at       
bitcoin in Runaway exception       



************************
EXCEPTION: St12out_of_range       
map::at       
bitcoin in Runaway exception       

bitcoin-qt: ./checkqueue.h:204: CCheckQueue<CScriptCheck>::~CCheckQueue() [T = CScriptCheck]: Assertion `m_worker_threads.empty()' failed.
Aborted
```

> A fatal error occurred. Bitcoin Core can no longer continue safely and will quit.

To reproduce, a quick hack:

```c++
--- a/src/script/descriptor.cpp
+++ b/src/script/descriptor.cpp
@@ -1408,7 +1408,7 @@ std::unique_ptr<DescriptorImpl> ParseScript(uint32_t& key_exp_index, Span<const
         error = "Can only have addr() at top level";
         return nullptr;
     }
-    if (ctx == ParseScriptContext::TOP && Func("tr", expr)) {
+    if (ctx == ParseScriptContext::TOP && Func("trx", expr)) {
         auto arg = Expr(expr);
         auto internal_key = ParsePubkey(key_exp_index, arg, ParseScriptContext::P2TR, out, error);
         if (!internal_key) {
```
// Make a backup of the DB
    stdstring _name = ->GetName();
    fspath this__dir = fsabsolute(fsPathFromString(->GetDatabase().Filename())).parent_path();
    fspath backup_filename = fsPathFromString(strprintf("%s-%d.legacy.bak", _name, GetTime()));
    fspath backup_path = this__dir / backup_filename;
    if (!->BackupWallet(fsPathToString(backup_path))) {
        return utilError{_("Error Unable to make a backup of your ")};
    }
    res.backup_path = backup_path;
    // Unload th so that nothing else tries to use it while we're changing it
    if (!RemoveWallet(context, , /*load_on_st, warnings)) {
        return utilError{_("Unable to unload th before migrating")};
    }
    UnloadWallet(stdmove());
    // Load th but only in the context of this function.
    // No signals should be connected nor should anything else be aware of this 
    WalletContext empty_context;
    empty_context.args = context.args;
    DatabaseOptions options;
    options.require_existing = true;
    DatabaseStatus status;
    stdunique_ptr<WalletDatabase> database = MakeWalletDatabase(_name, options, status, error);
    if (!database) {
        return utilError{Untranslated("Wallet file verification failed.") + Untranslated(" ") + error};
    }
    stdshared_ptr<CWallet> local_ = CWalletCreate(empty_context, _name, stdmove(database), options.create_flags, error, warnings);
    if (!local_) {
        return utilError{Untranslated("Wallet loading failed.") + Untranslated(" ") + error};
    }
    bool success = false;