fix(carousel): reset $currentTransition when no slides

[wesleycho]

• Reset $currentTransition when there are no slides

Here is a Plunker with the fix in action (as well as fixes to user error).

This fixes #4390.

[Foxandxss]

When creating a Plunker, please add instructions of how to see it working. If I understood correctly, I need to delete all slides and add new ones, but I don't see how to do that in the plunker.

[wesleycho]

The Plunker is resetting it at a setTimeout of 5000ms, which is coincidentally when the animation starts, which triggers the bug in the original Plunker in the referenced issue

[Foxandxss]

I see. After some seconds (before doing the first change) it does a weird animation thing. Do you see that? (Chrome).

[wesleycho]

Yep, that will be hard to fix I think - there is another issue open currently with the 0.14 milestone on a weird animation problem when adding a new slide though, may be slightly related

[Foxandxss]

Alright then.