Fix a bug where non-cropped layer could be scaled incorrectly

If a layer is not cropped but its bounds are outside of the
viewport (i.e.: clipped), the crop rectangle passed to
hw composer would be invalid because it started invalid
in the first place (to indicate "no crop").

Bug: 10410944
Change-Id: I4ae4d49a1adef0be7fa4304ecf84b1a5b7d03fe0