TwoTime throws an exception when the TP task effort is unset

Found by Kal Swan:

<img width="1451" height="335" alt="Image" src="https://github.com/user-attachments/assets/73038692-1454-4483-a356-1fb98adea7fc" />

"I think the problem was just that my task didn't have an effort against it. After doing that it seems to be fine now."