Vulkan: prevent volk reloading on null instance and devices

Bug: angleproject:4419
Change-Id: I82f9bb157e88754efd074358dccef1bb82cab0f7
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2068902
Reviewed-by: Tobin Ehlis <tobine@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>

src/libANGLE/renderer/vulkan/RendererVk.cpp

diff --git a/src/libANGLE/renderer/vulkan/RendererVk.cpp b/src/libANGLE/renderer/vulkan/RendererVk.cpp
index ab712f5..2ad3034 100644
--- a/src/libANGLE/renderer/vulkan/RendererVk.cpp
+++ b/src/libANGLE/renderer/vulkan/RendererVk.cpp
@@ -2048,12 +2048,12 @@
 
 void RendererVk::reloadVolkIfNeeded() const
 {
-    if (volkGetLoadedInstance() != mInstance)
+    if ((mInstance != VK_NULL_HANDLE) && (volkGetLoadedInstance() != mInstance))
     {
         volkLoadInstance(mInstance);
     }
 
-    if (volkGetLoadedDevice() != mDevice)
+    if ((mDevice != VK_NULL_HANDLE) && (volkGetLoadedDevice() != mDevice))
     {
         volkLoadDevice(mDevice);
     }