Empty if/elseif/else statements should have a "pass"

```
class Klass {
    void method() {
        if (true) {
        }
        else if (false) {}
        else {}
    }
}
```

The if statement is converted to:

```
if True:
elif False:
else
```

Which is invalid syntax, potential fix: https://gist.github.com/87c16eef54496e99b8ef
