Check item in OfflinePageTabHelper::LoadData

Some crash show that item can be nil.

Bug: 942292
Change-Id: I2ab962e02bf09d0224baab62abb2145579a51c8d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1605988
Commit-Queue: Olivier Robin <olivierrobin@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662130}
2 files changed