Screen.save_current must return the promise from display

When changing with next/previous from a modified record and save it, it can
lead to the Screen.display is applied after the change of record but with the
other record values.

src/screen.js

@@ -948,7 +948,7 @@
                 }.bind(this));
             }
             var display = function() {
-                this.display();
+                return this.display();
             }.bind(this);
             return prm.then(display, display);
         },