Vulkan: Ensure FramebufferVk::mRasterizationSamples > 0 GraphicsPipelineDesc can't handle samples being zero. This CL ensures we always use at least one sample. Bug: angleproject:431250668 Change-Id: I7f6b14c6060585fe7ef6fb55ed6a4b9813634f3f Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6431827 Reviewed-by: Yuxin Hu <yuxinhu@google.com> Commit-Queue: Charlie Lao <cclao@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>