The prior check was incorrectly validating a shard index of zero
and a shard count of one as inconsistent.

Bug: angleproject:3162
Change-Id: I63184c16e82f08080b275672a43e6dacf291560d
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2419045Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>