[FIX] #921 Fixed issue when discard a modal with draggable element

web_dialog_size/static/src/js/web_dialog_size.js

@@ -36,9 +36,11 @@ Dialog.include({
     },
 
     close: function() {
-        var draggable = this.$modal.draggable( "instance" );
-        if (draggable) {
-            this.$modal.draggable("destroy");
+        if (this.$modal) {
+            var draggable = this.$modal.draggable("instance");
+            if (draggable) {
+                this.$modal.draggable("destroy");
+            }
         }
         return this._super.apply(this, arguments);
     },