perf evsel: Avoid container_of on a NULL leader

An evsel should typically have a leader of itself, however, in tests
like 'Sample parsing' a NULL leader may occur and the container_of
will return a corrupt pointer.

Avoid this with an explicit NULL test.

Fixes: fba7c86601 ("libperf: Move 'leader' from tools/perf to perf_evsel::leader")
Reviewed-by: James Clark <james.clark@linaro.org>
Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Athira Rajeev <atrajeev@linux.ibm.com>
Cc: Blake Jones <blakejones@google.com>
Cc: Chun-Tse Shao <ctshao@google.com>
Cc: Collin Funk <collin.funk1@gmail.com>
Cc: Howard Chu <howardchu95@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jan Polensky <japo@linux.ibm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Li Huafei <lihuafei1@huawei.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Nam Cao <namcao@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steinar H. Gunderson <sesse@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20250821163820.1132977-4-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evsel.c

@@ -3935,6 +3935,8 @@ bool evsel__is_hybrid(const struct evsel *evsel)
 
 struct evsel *evsel__leader(const struct evsel *evsel)
 {
+	if (evsel->core.leader == NULL)
+		return NULL;
 	return container_of(evsel->core.leader, struct evsel, core);
 }