parser drops remaining rules on extra invalid closing brace

# Problem

```
var result = parse('foo { color: red; }} bar { color: blue; }')
console.log(result.stylesheet.rules.length)
// 1
```

All rules following an extra invalid closing brace get dropped.
# Expected
- In normal mode: an `Error` should be thrown: ~ `Extra closing brace`.
- In `silent` mode: the invalid brace should be removed, and the parsing should continue correctly.
