Prevent empty images from passing rasterization tests

Prevent empty images from passing rasterization tests

Some of the rasterization tests passed even when skipping
primitive drawing. Narrow lines had only edge pixels and
those are not verified because the implementations may
vary. Now a sanity check is performed in all cases to
prevent empty results from passing.

New tests:

dEQP-VK.rasterization.*
dEQP-GLES*.functional.rasterization.*

Components: Framework, Vulkan, OpenGL ES

VK-GL-CTS issue: 2168

Change-Id: I8df0a7a9490253e1f825697420b22cd9f15f3986