anv/descriptor_set: Only vma_heap_finish if we have a descriptor buffer

Fixes: 7bb34ecff9 "anv: release memory allocated by bo_heap when..."
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>

src/intel/vulkan/anv_descriptor_set.c

@@ -754,11 +754,10 @@ void anv_DestroyDescriptorPool(
       anv_gem_munmap(pool->bo.map, pool->bo.size);
       anv_vma_free(device, &pool->bo);
       anv_gem_close(device, pool->bo.gem_handle);
+      util_vma_heap_finish(&pool->bo_heap);
    }
    anv_state_stream_finish(&pool->surface_state_stream);
 
-   util_vma_heap_finish(&pool->bo_heap);
-
    vk_free2(&device->alloc, pAllocator, pool);
 }