bytes: improve readability of IndexAny and LastIndexAny functions
bytes: improve readability of IndexAny and LastIndexAny functions

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 <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

Cofyc/go,josharian/go,golang/go,CAFxX/go,nawawi/go,polyverse-security/go,golang/go,akutz/go,cloudflare/go,akutz/go,polyverse-security/go,CAFxX/go,nawawi/go,golang/go,CAFxX/go,cloudflare/go,akutz/go,codestation/go,cloudflare/go,codestation/go,codestation/go,Cofyc/go,cloudflare/go,polyverse-security/go,golang/go,cloudflare/go,Cofyc/go,christopher-henderson/Go,Cofyc/go,josharian/go,cloudflare/go,josharian/go,josharian/go,nawawi/go,nawawi/go,josharian/go,codestation/go,Cofyc/go,CAFxX/go,CAFxX/go,Cofyc/go,Cofyc/go,polyverse-security/go,golang/go,polyverse-security/go,codestation/go,akutz/go,Cofyc/go,cloudflare/go,nawawi/go,akutz/go,josharian/go,polyverse-security/go,nawawi/go,nawawi/go,akutz/go,golang/go,josharian/go,polyverse-security/go,codestation/go,CAFxX/go,codestation/go,golang/go,codestation/go,golang/go,cloudflare/go,akutz/go,akutz/go,nawawi/go,polyverse-security/go,CAFxX/go,CAFxX/go,josharian/go