git-codereview: do not install hooks for help and invalid commands
git-codereview: do not install hooks for help and invalid commands

Fixes golang/go#34320

Change-Id: I53348a027d1a33d1614d2bad32c75eaca52fac8a
Reviewed-on: https://go-review.googlesource.com/c/review/+/195897
Run-TryBot: Daniel Martí <29bf28b42a938ace12a5819da4ed4ba03d82f315@mvdan.cc>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Daniel Martí <29bf28b42a938ace12a5819da4ed4ba03d82f315@mvdan.cc>

golang/review