Readd a feature lost in pw(8) refactoring

pw usermod foo -m

It used to be able to (re)create the home directory if it didn't exists

PR:		216224
Reported by:	ae
MFC after:	3 days

usr.sbin/pw/pw_user.c

@@ -1697,6 +1697,10 @@ pw_user_mod(int argc, char **argv, char *arg1)
 		edited = true;
 	}
 
+	if (createhome && fstatat(conf.rootfd, pwd->pw_dir, &st, 0) == -1) {
+		docreatehome = true;
+	}
+
 	if (homedir && strcmp(pwd->pw_dir, homedir) != 0) {
 		pwd->pw_dir = homedir;
 		edited = true;