perf evsel: Fix potential null pointer dereference in perf_evsel__new_idx()

If evsel is NULL, we should return NULL to avoid a NULL pointer
dereference a bit later in the code.

Signed-off-by: Hisao Tanabe <xtanabe@gmail.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Wang Nan <wangnan0@huawei.com>
Fixes: 03e0a7df3efd ("perf tools: Introduce bpf-output event")
LPU-Reference: 20180824154556.23428-1-xtanabe@gmail.com
Link: https://lkml.kernel.org/n/tip-e5plzjhx6595a5yjaf22jss3@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evsel.c

@@ -251,8 +251,9 @@ struct perf_evsel *perf_evsel__new_idx(struct perf_event_attr *attr, int idx)
 {
 	struct perf_evsel *evsel = zalloc(perf_evsel__object.size);
 
-	if (evsel != NULL)
-		perf_evsel__init(evsel, attr, idx);
+	if (!evsel)
+		return NULL;
+	perf_evsel__init(evsel, attr, idx);
 
 	if (perf_evsel__is_bpf_output(evsel)) {
 		evsel->attr.sample_type |= (PERF_SAMPLE_RAW | PERF_SAMPLE_TIME |