options parser exception parsing multiple options in same code block

A proto file with options like:

```
option (toplevel_3.options) = {
  opt1: true,
  opt2: "Support multiple options in the same block"
};
```

Causes exceptions when parsing: 

```
 Parse error at line 5: illegal option name: (toplevel_3.options).,
    Error: Parse error at line 5: illegal option name: (toplevel_3.options).,
```
