debugger: count space for line numbers correctly

Fixed weird behaviour of line numbers around 50th, 950th, 9950th line:

```
break in script:50
 48     }
 49 }
  50 debugger;
  51 if (!config.user_agent) config.user_agent = 'package/'+pkg.version;
  52 if (!config.self_path) config.self_path = config_path;
```

Also, one less TODO in the code now which is usually a good thing.