Fix uninitlized variable

This bug may lead to incorrectly detect extra labels.

BUG=chromium:387571
TEST=tested on more machines manually

Change-Id: If834b7bd44a365814836b750657f125959f76a1d
Previous-Reviewed-on: https://chromium-review.googlesource.com/205211
(cherry picked from commit b6043545266a6d484990a5815f80489d8309fc69)
Reviewed-on: https://chromium-review.googlesource.com/205741
Reviewed-by: Wu-Cheng Li <wuchengli@chromium.org>
Commit-Queue: Kuang-che Wu <kcwu@chromium.org>
Tested-by: Kuang-che Wu <kcwu@chromium.org>
1 file changed