[Perf bug-fix] check null of sym pointer before using it

[Shan Wei <shanwei88@gmail.com>]

From: Samuel Liao <samuelliao@tencent.com>

Sometimes, sym will be null that causing perf crash.

Signed-off-by: Shan Wei <davidshan@tencent.com>
---
 tools/perf/ui/browsers/annotate.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/tools/perf/ui/browsers/annotate.c b/tools/perf/ui/browsers/annotate.c
index 4deea6a..50873a8 100644
--- a/tools/perf/ui/browsers/annotate.c
+++ b/tools/perf/ui/browsers/annotate.c
@@ -814,7 +814,7 @@ int symbol__tui_annotate(struct symbol *sym, struct map *map, int evidx,
 {
 	struct disasm_line *pos, *n;
 	struct annotation *notes;
-	const size_t size = symbol__size(sym);
+	size_t size;
 	struct map_symbol ms = {
 		.map = map,
 		.sym = sym,
@@ -834,6 +834,8 @@ int symbol__tui_annotate(struct symbol *sym, struct map *map, int evidx,
 	if (sym == NULL)
 		return -1;
 
+	size = symbol__size(sym);
+
 	if (map->dso->annotate_warned)
 		return -1;
 
-- 
1.7.1