HWC2: Don't set null handle for client layers am: 6be00284

        // setup a solid color layer yet

        ALOGV("[%s] Requesting Client composition", mName.string());

        setCompositionType(hwcId, HWC2::Composition::Client);

        error = hwcLayer->setBuffer(nullptr, Fence::NO_FENCE);

        if (error != HWC2::Error::None) {

            ALOGE("[%s] Failed to set null buffer: %s (%d)", mName.string(),

                    to_string(error).c_str(), static_cast<int32_t>(error));

        }

        return;

    }