perf branch: Avoid incrementing NULL

[ Upstream commit c969a9d ]

If the entry is NULL the value is meaningless so early return NULL to
avoid an increment of NULL. This was happening in calls from
has_stitched_lbr when running the "perf record LBR tests". The return
value isn't used in that case, so returning NULL as no effect.

Fixes: 42bbabe ("perf tools: Add hw_idx in struct branch_stack")
Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: captain5050

tools/perf/util/branch.h

@@ -66,6 +66,9 @@ static inline struct branch_entry *perf_sample__branch_entries(struct perf_sampl
 {
 	u64 *entry = (u64 *)sample->branch_stack;
 
+	if (entry == NULL)
+		return NULL;
+
 	entry++;
 	if (sample->no_hw_idx)
 		return (struct branch_entry *)entry;