util/vk_alloc: Ensure NULL is handled correctly in vk_free

Reviewed-by: Dave Airlie <airlied@redhat.com>

src/util/vk_alloc.h

@@ -46,6 +46,9 @@ vk_realloc(const VkAllocationCallbacks *alloc,
 static inline void
 vk_free(const VkAllocationCallbacks *alloc, void *data)
 {
+   if (data == NULL)
+      return;
+
    alloc->pfnFree(alloc->pUserData, data);
 }