rebase: finish_rebase() in noop rebase

In the following case

  $ git rebase master
  Current branch autostash-fix is up to date.

the autostash is not applied automatically, because this codepath
forgets to call finish_rebase().  Fix this.  Also add a test to guard
against regressions.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-rebase.sh

@@ -547,6 +547,7 @@ then
 		# Lazily switch to the target branch if needed...
 		test -z "$switch_to" || git checkout "$switch_to" --
 		say "$(eval_gettext "Current branch \$branch_name is up to date.")"
+		finish_rebase
 		exit 0
 	else
 		say "$(eval_gettext "Current branch \$branch_name is up to date, rebase forced.")"

t/t3420-rebase-autostash.sh

@@ -152,6 +152,17 @@ test_expect_success "rebase: fast-forward rebase" '
 	git checkout feature-branch
 '
 
+test_expect_success "rebase: noop rebase" '
+	test_config rebase.autostash true &&
+	git reset --hard &&
+	git checkout -b same-feature-branch feature-branch &&
+	test_when_finished git branch -D same-feature-branch &&
+	echo dirty >>file1 &&
+	git rebase feature-branch &&
+	grep dirty file1 &&
+	git checkout feature-branch
+'
+
 testrebase "" .git/rebase-apply
 testrebase " --merge" .git/rebase-merge
 testrebase " --interactive" .git/rebase-merge