glsl/images: bounds check image unit assignment

glsl/images: bounds check image unit assignment

The CTS test:
GL45-CTS.multi_bind.dispatch_bind_image_textures
binds 192 image uniforms, we reject this later,
but not until after we trash the contents of the
struct gl_shader.

Error now reads:
Too many compute shader image uniforms (192 > 16)
instead of
Too many compute shader image uniforms (2745344416 > 16)

Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: "12.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>