[PATCH] perf hists browser: Fix segfault when all entries be filtered

[He Kuang]

When all perf report entries be filtered, the result of
hists__filter_entries() can be NULL, check the result before processing.

Miss this checking will cause segmentation fault like this:

  $ perf report

(filter all entries and left nothing, then zoom in/out)
  perf: Segmentation fault
  -------- backtrace --------
  ../bin/perf[0x4d1858]
  ../lib64/libc.so.6(+0x3545f)[0x7fe72fc1145f]
  ../bin/perf[0x4cd9f5]
  ../bin/perf[0x4ce176]
  ../bin/perf[0x4d0506]
  ../bin/perf[0x41a94f]
  ../bin/perf[0x408cf2]
  ../bin/perf[0x408455]
  ../lib64/libc.so.6(__libc_start_main+0xf4)[0x7fe72fbfdbd4]
  ../bin/perf[0x408584]

Signed-off-by: He Kuang <hekuang@xxxxxxxxxx>
---
 tools/perf/ui/browsers/hists.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/perf/ui/browsers/hists.c b/tools/perf/ui/browsers/hists.c
index 788506e..1106bb8 100644
--- a/tools/perf/ui/browsers/hists.c
+++ b/tools/perf/ui/browsers/hists.c
@@ -992,6 +992,9 @@ static void ui_browser__hists_seek(struct ui_browser *browser,
 	 * and stop when we printed enough lines to fill the screen.
 	 */
 do_offset:
+	if (!nd)
+		return;
+
 	if (offset > 0) {
 		do {
 			h = rb_entry(nd, struct hist_entry, rb_node);
-- 
2.2.0.33.gc18b867

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