pvr: Add missing NULL checks in some vkDestroy...() functions

pvr: Add missing NULL checks in some vkDestroy...() functions

Seems like `dEQP-VK.api.null_handle.destroy_device` was already
passing but let's add the null check in case of future changes
which might not accept NULL.

Fixes:
  dEQP-VK.api.null_handle.destroy_descriptor_set_layout
  dEQP-VK.api.null_handle.destroy_pipeline_layout
  dEQP-VK.api.null_handle.destroy_query_pool

Signed-off-by: Karmjit Mahil <Karmjit.Mahil@imgtec.com>
Reviewed-by: Frank Binns <frank.binns@imgtec.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22918>