Compiler crash: decorator called with return type Model when extern fn argument is an invalid reference

## Bug Report

When an `extern fn` is called with an invalid reference as an argument, the compiler does not call the function (correct), but still calls the decorator with the function's **declared return type** (the `Reflection.Operation` Model) instead of skipping the decorator application or reporting an error gracefully.

This causes an internal compiler crash.

### Minimal Repro

**main.tsp**
```tsp
import "./test.js";

#suppress "experimental-feature" "testing extern fn crash with invalid ref"
extern fn myFn(target: Reflection.Operation): Reflection.Operation;

extern dec myDec(target: Reflection.Operation, override: Reflection.Operation);

op test(): void;

@@myDec(test, myFn(invalidref));
```

**test.js**
```js
// @ts-check

export const $functions = {
"": {
myFn: (context, target) => {
console.log("BUG: myFn was called despite invalid reference argument");
return target;
},
},
};

export const $myDec = (context, target, override) => {
console.log("$myDec called");
console.log(" target:", target?.kind, target?.name);
console.log(" override:", override?.kind, override?.name);
override.parameters.properties;
};
```

### Observed Behavior

```
$myDec called
target: Operation test
override: Model Operation ← WRONG: should be an Operation, not the type Model
Internal compiler error!
TypeError: Cannot read properties of undefined (reading 'properties')
at $myDec (test.js)
at applyDecoratorToType (checker.ts:8646)
```

The decorator `$myDec` is called with `override` being the `Reflection.Operation` **Model type** (kind: "Model", name: "Operation") — the declared return type of `myFn` — instead of an actual `Operation` instance.

### Expected Behavior

When the function call `myFn(invalidref)` fails due to an invalid reference:
- The decorator should **not** be applied (since its argument could not be resolved), OR
- An error diagnostic should be reported and the decorator call skipped

The compiler should never pass the raw return type declaration as a decorator argument.

### Stack Trace

```
TypeError: Cannot read properties of undefined (reading 'properties')
at $myDec (test.js:20:23)
at applyDecoratorToType (checker.ts:8646:12)
at applyDecoratorsToType (checker.ts:7919:26)
at finishType (checker.ts:7903:30)
at finishOperation (checker.ts:2667:14)
```

### Real-world Impact

This is triggered by `@@override(test, reorderParameters(abcde, #["b", "a"]))` in `@azure-tools/typespec-client-generator-core` where `abcde` is a typo/invalid reference. The `$override` decorator crashes at `override.parameters.properties`.

### Version

TypeSpec compiler v1.12.0