prevent administrators from being deleted - first remove them from admin group

src/socket.io/admin/user.js

@@ -98,6 +98,11 @@ User.deleteUsers = function(socket, uids, callback) {
 	}
 
 	async.each(uids, function(uid, next) {
+		user.isAdministrator(uid, function(err, isAdmin) {
+			if (err || isAdmin) {
+				return callback(err || new Error('[[error:cant-ban-other-admins]]'));
+			}
+
 			user.delete(uid, function(err) {
 				if (err) {
 					return next(err);
@@ -108,6 +113,7 @@ User.deleteUsers = function(socket, uids, callback) {
 				websockets.logoutUser(uid);
 				next();
 			});
+		});
 	}, callback);
 };