D3D9: Write dummy output for depth/stencil only draw. This prevents a spurious D3D runtime warning, which was clogging up some of our test output. BUG=angleproject:1660 Change-Id: I1a747ba7532323b989dbed1ee7c78b3b457768a6 Reviewed-on: https://chromium-review.googlesource.com/437724 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>