Check if fence is nullptr in PostHandleQueueSignal

PostHandleQueueSignal assumed that fence was not null because QueueSignal
generates an error if it is. The errors are not surfaced immediately so
this additional check is needed before doing the post-handler.

Bug: chromium:914808
Change-Id: I2a99f5229712d49d3c9a2d1f3f2dd1009247a24c
Reviewed-on: https://dawn-review.googlesource.com/c/3280
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

generator/templates/dawn_wire/WireServer.cpp

diff --git a/generator/templates/dawn_wire/WireServer.cpp b/generator/templates/dawn_wire/WireServer.cpp
index 34a2daa..833f154 100644
--- a/generator/templates/dawn_wire/WireServer.cpp
+++ b/generator/templates/dawn_wire/WireServer.cpp
@@ -509,6 +509,9 @@
                 {% set custom_post_handler_commands = ["QueueSignal"] %}
 
                 bool PostHandleQueueSignal(const QueueSignalCmd& cmd) {
+                    if (cmd.fence == nullptr) {
+                        return false;
+                    }
                     ObjectId fenceId = mFenceIdTable.Get(cmd.fence);
                     ASSERT(fenceId != 0);
                     auto* fence = mKnownFence.Get(fenceId);

src/dawn_native/Fence.cpp

diff --git a/src/dawn_native/Fence.cpp b/src/dawn_native/Fence.cpp
index 7906c38..54ed9a9 100644
--- a/src/dawn_native/Fence.cpp
+++ b/src/dawn_native/Fence.cpp
@@ -18,7 +18,6 @@
 #include "dawn_native/Device.h"
 #include "dawn_native/ValidationUtils_autogen.h"
 
-#include <cstdio>
 #include <utility>
 
 namespace dawn_native {