When constructing a Graphics pipeline, some structures may or may
not exist, depending on what will be used by the render pass. These
structures (viewportState, multisampleState, depthStencilState and
colorBlendState) are now checked before being used, since it is
allowed for these to be null.

Bug b/118386749

Change-Id: If2759ae2554a98143b30e70624a0dc8d88c5bd43
Reviewed-on: https://swiftshader-review.googlesource.com/c/24911Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>