perf session: 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-dyuupcj0hnoyt96vma8b3anv@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-buildid-cache.c

@@ -419,7 +419,6 @@ int cmd_buildid_cache(int argc, const char **argv,
 		pr_warning("Couldn't add %s\n", kcore_filename);
 
 out:
-	if (session)
 	perf_session__delete(session);
 
 	return ret;

tools/perf/builtin-diff.c

@@ -756,9 +756,7 @@ static int __cmd_diff(void)
 
  out_delete:
 	data__for_each_file(i, d) {
-		if (d->session)
 		perf_session__delete(d->session);
-
 		data__free(d);
 	}
 

tools/perf/builtin-kvm.c

@@ -1426,7 +1426,6 @@ static int kvm_events_live(struct perf_kvm_stat *kvm,
 	err = kvm_events_live_report(kvm);
 
 out:
-	if (kvm->session)
 	perf_session__delete(kvm->session);
 	kvm->session = NULL;
 	perf_evlist__delete(kvm->evlist);

tools/perf/util/session.c

@@ -178,6 +178,8 @@ static void perf_session__delete_threads(struct perf_session *session)
 
 void perf_session__delete(struct perf_session *session)
 {
+	if (session == NULL)
+		return;
 	auxtrace__free(session);
 	auxtrace_index__free(&session->auxtrace_index);
 	perf_session__destroy_kernel_maps(session);