perf evlist: Destructors should accept NULL

And do nothing, just like free(), to avoid having to test it in callers,
usually in error paths.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-mexbavy0ft387j5w89t365eu@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/event-times.c

@@ -200,8 +200,7 @@ static int test_times(int (attach)(struct perf_evlist *),
 		 count.ena, count.run);
 
 out_err:
-	if (evlist)
-		perf_evlist__delete(evlist);
+	perf_evlist__delete(evlist);
 	return !err ? TEST_OK : TEST_FAIL;
 }