anv: fix crash in vkCmdClearAttachments with unused attachment
anv_render_pass_compile() turns an unused attachment into a NULL depth_stencil_attachment pointer so check that pointer before accessing it.
Found with updates to existing CTS tests.
Signed-off-by: Lionel Landwerlin lionel.g.landwerlin@intel.com Fixes: 208be8ea ("anv: Make subpass::depth_stencil_attachment a pointer")