### 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.
reduce_expression(p_unary_op->operand);
	GDScriptParser::DataType result;
	if (p_unary_op->operand == nullptr) {
		result.kind = GDScriptParser::DataType::VARIANT;
		p_unary_op->set_datatype(result);
		return;
	}
	GDScriptParser::DataType operand_type = p_unary_op->operand->get_datatype();
	if (p_unary_op->operand->is_constant) {
		p_unary_op->is_constant = true;
		p_unary_op->reduced_value = Variant::evaluate(p_unary_op->variant_op, p_unary_op->operand->reduced_value, Variant());
		result = type_from_variant(p_unary_op->reduced_value, p_unary_op);
	}
	if (operand_type.is_variant()) {
		result.kind = GDScriptParser::DataType::VARIANT;
		mark_node_unsafe(p_unary_op);
	} else {
		bool valid = false;
		result = get_operation_type(p_unary_op->variant_op, operand_type, valid, p_unary_op);
		if (!valid) {
			push_error(vformat(R"(Invalid operand of type "%s" for unary operator "%s".)", operand_type.to_string(), Variant::get_operator_name(p_unary_op->variant_op)), p_unary_op);
		}
	}
	p_unary_op->set_datatype(result);
}
Variant GDScriptAnalyzer::make_expression_reduced_value(GDScriptParser::ExpressionNode *p_expression, bool &is_reduced) {