perf script: Check output fields only for samples

There's no need to check sampling output fields for events without
perf_event_attr::sample_type field set.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Kan Liang <kan.liang@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1444992092-17897-51-git-send-email-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-script.c

@@ -686,7 +686,10 @@ static int process_attr(struct perf_tool *tool, union perf_event *event,
 
 	set_print_ip_opts(&evsel->attr);
 
-	return perf_evsel__check_attr(evsel, scr->session);
+	if (evsel->attr.sample_type)
+		err = perf_evsel__check_attr(evsel, scr->session);
+
+	return err;
 }
 
 static int process_comm_event(struct perf_tool *tool,