Fix TaskView scale being 0

Before, we reset zoom scale to 1 but didn't reset curve scale. Thus,
if curve scale had never been set (i.e. we hadn't yet scrolled recents),
the task view scale would be 0.

Example problem:
1. Open Calculator or other app
2. Force stop launcher
3. Swipe up
The recents-scale-down animation was incorrect because the computed scale
was 0, and thus recents didn't scale down at all throughout the swipe.

Change-Id: I8dd3c73a231033fa633e8df2df3bf9a1c0a67263