Don't refuse to rewrite source file if rewriters are actually used.

At the end of the `@rewriters.each` loop, the value of `buffer.name` is no longer valid due to debugging annotations:

```ruby
        new_buffer = Source::Buffer.new(initial_buffer.name +
                                    '|after ' + rewriter_class.name)
```

This preserves the original name, allowing the file to be properly rewritten.