Avoid null LBR and callchain pointers in sample info

BUG=none
TEST=unit tests pass

Change-Id: Id57505337b4d0a3743367b3f2e563a948bda8548
Signed-off-by: Simon Que <sque@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/196628
Reviewed-by: Emma Rapati <rapati@chromium.org>
1 file changed