mesa: Skip partial InvalidateFramebuffer of packed depth/stencil.
One of the CTS cases tries to invalidate just stencil of packed depth/stencil, and we incorrectly lost the depth contents.
Fixes dEQP-GLES3.functional.fbo.invalidate.whole.unbind_read_stencil Fixes: 0c42b5f3 ("mesa: wire up InvalidateFramebuffer")