pw: fix uninitialized name pointer in pw_group_del

The 'name' variable could be left uninitialized if neither the
positional argument nor -n is supplied, leading to undefined
behavior when passed to getgroup().

usr.sbin/pw/pw_group.c

@@ -367,7 +367,7 @@ pw_group_del(int argc, char **argv, char *arg1)
 {
 	struct userconf *cnf = NULL;
 	struct group *grp = NULL;
-	char *name;
+	char *name = NULL;
 	const char *cfg = NULL;
 	intmax_t id = -1;
 	int ch, rc;

usr.sbin/pw/tests/pw_groupdel_test.sh

@@ -18,6 +18,20 @@ group_do_not_delete_wheel_if_group_unknown_body() {
 }
 
 
-atf_init_test_cases() {
-        atf_add_test_case group_do_not_delete_wheel_if_group_unknown
+atf_test_case group_delete_by_gid cleanup
+group_delete_by_gid_head() {
+	atf_set "descr" "Test deleting a group by gid without providing a name"
+}
+group_delete_by_gid_body() {
+	populate_etc_skel
+	${PW} groupadd testgroup -g 1000 || atf_fail "Creating test group"
+	atf_check -s exit:0 -o inline:"testgroup:*:1000:\n" \
+		-x ${PW} groupshow 1000
+	${PW} groupdel -g 1000 || atf_fail "Deleting group by gid"
+}
+
+
+atf_init_test_cases() {
+	atf_add_test_case group_do_not_delete_wheel_if_group_unknown
+	atf_add_test_case group_delete_by_gid
 }