text/template/parse: remove duplication in peekNonSpace
text/template/parse: remove duplication in peekNonSpace

nextNonSpace has an identical code except the call to
backup at the end.

Change-Id: Iefa5b13950007da38323a800fb6b0ce3d436254b
Reviewed-on: https://go-review.googlesource.com/c/go/+/198277
Run-TryBot: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

golang/go,akutz/go,CAFxX/go,akutz/go,golang/go,CAFxX/go,cloudflare/go,cloudflare/go,golang/go,akutz/go,cloudflare/go,cloudflare/go,nawawi/go,nawawi/go,nawawi/go,CAFxX/go,akutz/go,golang/go,golang/go,golang/go,golang/go,nawawi/go,CAFxX/go,cloudflare/go,cloudflare/go,nawawi/go,golang/go,nawawi/go,CAFxX/go,akutz/go,akutz/go,CAFxX/go,CAFxX/go,akutz/go,cloudflare/go,CAFxX/go,nawawi/go,akutz/go,cloudflare/go,nawawi/go