Fixes assert when ReadPixels() called to read from FBO to GL_PIXEL_PACK_BUFFER, on mip-level > 0, since num_layers wasn't properly calculated with mip-level.
The logic of fix is similar to one in 'update_image_surface' function of i965 driver, which is introduced in commit f9fd0cf4, and called in similar circumstances.
Closes: Fixes:
Signed-off-by: Yevhenii Kharchenko yevhenii.kharchenko@globallogic.com