Merge pull request #997 from Tardo/fix#981

[11.0][FIX] web_dialog_size: Draggable Dialog

web_dialog_size/static/src/js/web_dialog_size.js

@@ -26,15 +26,15 @@ Dialog.include({
         });
     },
 
-    open: function() {
-        this._super.apply(this, arguments);
+    opened: function(handler) {
+        return this._super.apply(this, arguments).then(function(){
             if (this.$modal) {
                 this.$modal.draggable({
                     handle: '.modal-header',
                     helper: false
                 });
             }
-        return this;
+        }.bind(this));
     },
 
     close: function() {