Vulkan: Fix segv referencing contextVk

Tests dEQP-EGL.functional.fence_sync.* can cause SyncHelper::clientWait
to be called with a null contextVk which we were trying to deference to
get to the renderer. We have a pointer to the renderer already so just
use that.

Bug: b/154030730
Change-Id: If64ec2c960f39b893d2e47a11638d16f830aecfd
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2493181
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>

src/libANGLE/renderer/vulkan/SyncVk.cpp

@@ -108,9 +108,9 @@ angle::Result SyncHelper::clientWait(Context *context,
 
     // If we are using worker need to wait for the commands to be issued before waiting on the
     // fence.
-    if (contextVk->getRenderer()->getFeatures().enableCommandProcessingThread.enabled)
+    if (renderer->getFeatures().enableCommandProcessingThread.enabled)
     {
-        contextVk->getRenderer()->waitForCommandProcessorIdle(contextVk);
+        renderer->waitForCommandProcessorIdle(contextVk);
     }
 
     // Wait on the fence that's expected to be signaled on the first vkQueueSubmit after