perf tools: Release session and symbol resources on exit

So that we reduce the noise when looking for leaks using tools such as
valgrind.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index 8151d23..6b0db55 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -515,12 +515,13 @@
 	if (machine == NULL)
 		goto out_problem;
 	thread = perf_session__findnew(session, self->mmap.pid);
+	if (thread == NULL)
+		goto out_problem;
 	map = map__new(&machine->user_dsos, self->mmap.start,
 			self->mmap.len, self->mmap.pgoff,
 			self->mmap.pid, self->mmap.filename,
 			MAP__FUNCTION);
-
-	if (thread == NULL || map == NULL)
+	if (map == NULL)
 		goto out_problem;
 
 	thread__insert_map(thread, map);