trace: allow image resource to be null

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/gallium/auxiliary/driver_trace/tr_dump_state.c

@@ -724,7 +724,7 @@ void trace_dump_image_view(const struct pipe_image_view *state)
    if (!trace_dumping_enabled_locked())
       return;
 
-   if(!state) {
+   if (!state || !state->resource) {
       trace_dump_null();
       return;
    }