Fix crash in CaptivePortalTabReloader

This CL adds a null check for the last committed NavigationEntry to fix
a crash in CaptivePortalTabReloader.

Bug: 857002
Change-Id: Ia26bd420cbee80958b3a74937ade9efb764ed03a
Reviewed-on: https://chromium-review.googlesource.com/1146657
Commit-Queue: Matt Menke <mmenke@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577919}
1 file changed