It doesn't change the outcome. It might have been useful at some point
to avoid Replace from doing work or allocating. However, nowadays the
func returns early without doing any work if Count returns 0.

Change-Id: Id69dc74042a6e39672b405016484db8b50f43d58
Reviewed-on: https://go-review.googlesource.com/62991
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dave Cheney <dave@cheney.net>