mesa: Fix region overlap conditions for rectangles with a shared edge

mesa: Fix region overlap conditions for rectangles with a shared edge

>From OpenGL 4.0 spec, section 4.3.2 "Copying Pixels":
"The pixels corresponding to these buffers are copied from the source
 rectangle bounded by the locations (srcX0, srcY 0) and (srcX1, srcY 1)
 to the destination rectangle bounded by the locations (dstX0, dstY 0)
 and (dstX1, dstY 1). The lower bounds of the rectangle are inclusive,
 while the upper bounds are exclusive."

So, the rectangles sharing just an edge shouldn't overlap.
     -----------
    |           |
     ------- ---
    |       |   |
    |       |   |
     ------- ---

Cc: "12.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>