[ios] Made goToItemAtIndex: safe for release builds.

Changed -[CRWWebController goToItemAtIndex:] to make no-op on release if
index is out of bound. This fully mirrors
NavigationControllerImpl::GoToIndex, which calls NOTREACHED() and early
returns for out of bounds indices.

BUG=677160

Review-Url: https://codereview.chromium.org/2628133003
Cr-Commit-Position: refs/heads/master@{#443732}
1 file changed