Fixed problem when touch is cancelled by a multitouch gesture.

[bguidolim]

Situation:

• I limited user to edit rating from 1 up to 5, 0 is not an option;
• To limit it, I've implemented starsSelectionChanged:rating:protocol;
• When user drag to 0, it change to 1 again, but user can drag to 0 and without touch up, tap in another button so the rating will be 0.

This commit fix it.