perf_thread_map__nr returns length 1 if the perf_thread_map is NULL,
meaning index 0 is valid. When perf_thread_map__pid of index 0 is read
then return the expected "any" -1 value. Assert this is only done for
index 0.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/lib/perf/threadmap.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/lib/perf/threadmap.c b/tools/lib/perf/threadmap.c
index 07968f3ea093..3ca9ba4987fc 100644
--- a/tools/lib/perf/threadmap.c
+++ b/tools/lib/perf/threadmap.c
@@ -97,5 +97,10 @@ int perf_thread_map__nr(struct perf_thread_map *threads)
 
 pid_t perf_thread_map__pid(struct perf_thread_map *map, int idx)
 {
+	if (!map) {
+		assert(idx == 0);
+		return -1;
+	}
+
 	return map->map[idx].pid;
 }
-- 
2.49.0.1101.gccaa498523-goog