This change removes the check of len(chars) > 0 inside the Index and
IndexAny functions which was redundant.

Change-Id: Ic4bf8b8a37d7f040d3ebd81b4fc45fcb386b639a
Reviewed-on: https://go-review.googlesource.com/65851
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>