Fixing rounding error when computing bottom clip

- In TaskThumbnailView.updateThumbnailMatrix() we compare the rounded
  scaled bitmap height with the height of the task/thumbnail view.
  Since the position is also non-integer, the rounding of the sum
  is not equivalent to the rounding of the individual components, which
  causes the check to fail.

Bug: 135150767
Test: Quickswitch on sargo
Change-Id: I849b4732569e5b8699f00f5ff210f41fb505f1e7