Vulkan: Enable some more fbo.render dEQP tests Sometime we have a clear call with clearDepth+clearStencil but no attachment to clear. This was triggering the assert instead of just skipping the clear. Bug: angleproject:2597 Change-Id: I2d7750db919afe47cf02155f7c4afd0b02318bb1 Reviewed-on: https://chromium-review.googlesource.com/1106039 Commit-Queue: Luc Ferron <lucferron@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>