d3d12: Really handle null constant buffers

Previous attempt was checking the wrong pointer...

Fixes: eb27db86 ("d3d12: Handle null constant buffers")
Closes: #4362
Reviewed-by: Bill Kristiansen <billkris@microsoft.com>
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <!9349>
37 jobs for !9349 with runescape in 8 minutes and 37 seconds (queued for 2 seconds)
latest detached
Status Job ID Name Coverage
  Sanity
passed #8035826
sanity

00:00:08

 
  Container
passed #8035829
aarch64
arm_build

00:00:18

passed #8035830
arm_test-base

00:00:16

passed #8035831
windows shell 1809 mesa
windows_build_vs2019

00:00:09

passed #8035827
x86_build-base

00:00:15

passed #8035828
x86_test-base

00:00:15

 
  Container 2
passed #8035839
android_build

00:00:17

passed #8035842
arm64_test

00:00:14

passed #8035843
armhf_test

00:00:22

passed #8035836
i386_build

00:00:18

passed #8035832
kernel+rootfs_amd64

00:00:20

passed #8035833
aarch64
kernel+rootfs_arm64

00:01:07

passed #8035834
aarch64
kernel+rootfs_armhf

00:00:10

passed #8035837
ppc64el_build

00:00:19

passed #8035838
s390x_build

00:00:14

passed #8035835
x86_build

00:00:18

passed #8035840
x86_test-gl

00:00:16

passed #8035841
x86_test-vk

00:00:21

 
  Meson X86 64
passed #8035849
meson-clang

00:02:21

passed #8035850
meson-clover

00:02:12

passed #8035846
meson-clover-testing

00:02:22

passed #8035847
gstreamer
meson-gallium

00:01:51

passed #8035848
meson-release

00:01:31

passed #8035844
meson-testing

00:02:25

passed #8035845
meson-testing-asan

00:02:15

passed #8035851
meson-vulkan

00:02:20

 
  Build Misc
passed #8035852
meson-android

00:00:34

passed #8035854
aarch64
meson-arm64

00:01:35

passed #8035855
aarch64
meson-arm64-asan

00:02:51

passed #8035856
aarch64
meson-arm64-build-test

00:01:30

passed #8035853
aarch64
meson-armhf

00:01:36

passed #8035858
meson-i386

00:01:16

passed #8035861
meson-mingw32-x86_64

00:01:28

passed #8035860
kvm
meson-ppc64el

00:02:20

passed #8035859
kvm
meson-s390x

00:02:42

passed #8035857
windows docker 1809 mesa
meson-windows-vs2019

00:04:32

 
  Layered Backends
passed #8035862
windows docker 1809 mesa
test-d3d12-windows

00:03:40