D3D: No-op ClearBufferfi calls with no DS attachments.
D3D: No-op ClearBufferfi calls with no DS attachments.

The ES3 spec is clear that these calls should no-op, see page 187,

"If a buffer is not present, then a Clear directed at that buffer has
no effect."

BUG=angleproject:1078
TEST=dEQP-GLES3.functional.fbo.msaa.2_samples.*

Change-Id: Ic521f55785d10065e2ffe2e98a68c9d7da0c2c71
Reviewed-on: https://chromium-review.googlesource.com/286776
Reviewed-by: Corentin Wallez <470c533e86f4f848c98c7e11fffc2d043494a401@chromium.org>
Tested-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Reviewed-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>

ecoal95/angle,mybios/angle,crezefire/angle,mybios/angle,vvuk/angle,vvuk/angle,mikolalysenko/angle,MSOpenTech/angle,mikolalysenko/angle,bsergean/angle,larsbergstrom/angle,ppy/angle,csa7mdm/angle,mlfarrell/angle,ppy/angle,MSOpenTech/angle,ppy/angle,larsbergstrom/angle,vvuk/angle,bsergean/angle,bsergean/angle,crezefire/angle,domokit/waterfall,csa7mdm/angle,ecoal95/angle,mlfarrell/angle,domokit/waterfall,larsbergstrom/angle,mikolalysenko/angle,mybios/angle,vvuk/angle,ecoal95/angle,mybios/angle,csa7mdm/angle,larsbergstrom/angle,mikolalysenko/angle,csa7mdm/angle,ecoal95/angle,bsergean/angle,MSOpenTech/angle,MSOpenTech/angle,ecoal95/angle,crezefire/angle,mlfarrell/angle,crezefire/angle,ppy/angle,mlfarrell/angle