osmo-release.sh: Fix rc!=0 on TODO-RELEASE file without comment lines

Change-Id: Iff09a090284a0f65fd798d99265cba51f3309923
diff --git a/osmo-release.sh b/osmo-release.sh
index b4db440..b63f981 100755
--- a/osmo-release.sh
+++ b/osmo-release.sh
@@ -164,7 +164,7 @@
 
 set -e
 if [ -f "TODO-RELEASE" ]; then
-	grep '#' TODO-RELEASE > TODO-RELEASE.clean
+	grep '#' TODO-RELEASE > TODO-RELEASE.clean || true
 	mv TODO-RELEASE.clean TODO-RELEASE
 	git add TODO-RELEASE
 fi