SpirvShader: Fix int DBZ failures by masking away zeros.

SpirvShader: Fix int DBZ failures by masking away zeros.

The Vulkan spec says:
"division by zero produces an unspecified result but must not lead to Vulkan interruption or termination".

Tests: dEQP-VK.glsl.operator.binary_operator.mod.*
Tests: dEQP-VK.glsl.operator.binary_operator.div.*
Bug: b/127962486
Change-Id: I62e7c29a6e944512db7a8a96b0bb87488aa7be73
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/27171
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>