Cubemap textures are created with a border, which means that their
size is larger. Their range is also different. Instead of [0, dim-1],
they have a [-1, dim] range. This means that if we copy them starting
at [0, 0] for their full size, we'll overflow at the end, since the
buffer starts at [-1, -1]. This cl prevents going through the fast
copy path when we have a border.

Bug: chromium:1115345
Change-Id: I333acfd6094645231eb111634359d82ed3d5c787
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/47668
Presubmit-Ready: Alexis Hétu <sugoi@google.com>
Reviewed-by: Corentin Wallez <cwallez@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>