fix var use before definition
Otherwise you can get:
```
Traceback (most recent call last):
File "./compose_tracker.py", line 237, in <module>
c.__call__(m)
File "./compose_tracker.py", line 191, in __call__
kojitaskline, text = self.get_supporting_text([line])
File "./compose_tracker.py", line 125, in get_supporting_text
if not text:
UnboundLocalError: local variable 'text' referenced before assignment
```