anv: Handle null in all destructors

This fixes a bunch of new CTS tests which look for exactly this.  Even in
the cases where we just call vk_free to free a CPU data structure, we still
handle NULL explicitly.  This way we're less likely to forget to handle
NULL later should we actually do something less trivial.

Cc: "13.0" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Dave Airlie <airlied@redhat.com>

src/intel/vulkan/anv_pipeline_cache.c

@@ -454,6 +454,9 @@ void anv_DestroyPipelineCache(
    ANV_FROM_HANDLE(anv_device, device, _device);
    ANV_FROM_HANDLE(anv_pipeline_cache, cache, _cache);
 
+   if (!cache)
+      return;
+
    anv_pipeline_cache_finish(cache);
 
    vk_free2(&device->alloc, pAllocator, cache);