fix: recover conflict

lib/routes/page.js

@@ -643,15 +643,10 @@ module.exports = function(crowi, app) {
     .then(function(data) {
       pageData = data;
 
-      if (!req.form.isValid) {
-        debug('Form data not valid');
-        throw new Error('Form data not valid.');
-      }
-
       if (data && !data.isUpdatable(currentRevision)) {
         debug('Conflict occured');
-        req.form.errors.push('page_edit.notice.conflict');
-        throw new Error('Conflict.');
+        req.flash('dangerMessage', 'Conflict occured');
+        return res.redirect(req.headers.referer);
       }
 
       if (data) {