### Godot version

Beta 17, master

### System information

Windows 11

### Issue description

Godot gets a hard crash while attempting to code-complete for member `const` of a class.

### Steps to reproduce

```GDScript
enum E { V1 }

const e := E
```

And then type a `.` after the last `E`, which triggers code hints/auto-completion for subscripts based on `E` and causes a hard crash.

Does not happen for `var e := E.V1`.

### Minimal reproduction project

See above.
GDScriptParser::DataType nil_type;
	nil_type.builtin_type = Variant::NIL;
	nil_type.type_source = GDScriptParser::DataType::ANNOTATED_INFERRED;
	return get_operation_type(p_operation, p_a, nil_type, r_valid, p_source);
}
GDScriptParser::DataType GDScriptAnalyzer::get_operation_type(Variant::Operator p_operation, const GDScriptParser::DataType &p_a, const GDScriptParser::DataType &p_b, bool &r_valid, const GDScriptParser::Node *p_source) {
	Variant::Type a_type = p_a.builtin_type;
	Variant::Type b_type = p_b.builtin_type;