_cogl_texture_spans_foreach_in_region first swaps over the texture
coordinates if they are flipped so that it can always iterate in a
positive direction. It sets a flag so that it will remember that the
coordinates are flipped. Before invoking the callback it is meant to
reflip the coordinates so that the callee doesn't need to be aware of
the flipping. However it was only flipping the sub-texture coordinates
and not the virtual coordinates. This was causing sliced textures to
draw their slice rectangles with the wrong geometry.
test-backface-culling was failing because of this.
Reviewed-by: Robert Bragg <robert@linux.intel.com>
(cherry picked from commit e7338a1e09cb22151374aefa6f0bb58485af9189)
671275ba36