### 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.
if (!valid) {
				push_error(vformat(R"(Cannot get index "%s" from "%s".)", p_subscript->index->reduced_value, p_subscript->base->reduced_value), p_subscript->index);
				result_type.kind = GDScriptParser::DataType::VARIANT;
			} else {
				p_subscript->is_constant = true;
				p_subscript->reduced_value = value;
				result_type = type_from_variant(value, p_subscript);
			}
		} else {
			GDScriptParser::DataType base_type = p_subscript->base->get_datatype();
			GDScriptParser::DataType index_type = p_subscript->index->get_datatype();
			if (base_type.is_variant()) {
				result_type.kind = GDScriptParser::DataType::VARIANT;
				mark_node_unsafe(p_subscript);
			} else {
				if (base_type.kind == GDScriptParser::DataType::BUILTIN && !index_type.is_variant()) {
					
					bool error = index_type.kind != GDScriptParser::DataType::BUILTIN && base_type.builtin_type != Variant::DICTIONARY;
					if (!error) {
						switch (base_type.builtin_type) {
							
							case Variant::PACKED_BYTE_ARRAY:
							case Variant::PACKED_COLOR_ARRAY:
							case Variant::PACKED_FLOAT32_ARRAY:
							case Variant::PACKED_FLOAT64_ARRAY:
							case Variant::PACKED_INT32_ARRAY:
							case Variant::PACKED_INT64_ARRAY:
							case Variant::PACKED_STRING_ARRAY:
							case Variant::PACKED_VECTOR2_ARRAY:
							case Variant::PACKED_VECTOR3_ARRAY: