MAGETWO-90591: Add Selected Button shouldn't be enabled if there are no images available

- fix case that "Add Selected" button still appears after deleted selected image

Author: Joan He

lib/web/mage/adminhtml/browser.js

@@ -434,7 +434,7 @@ define([
                             showLoader: true
                         }).done($.proxy(function () {
                             self.reload();
-                            self.element.find('#delete_files').toggleClass(self.options.hidden, true);
+                            self.element.find('#delete_files, #insert_files').toggleClass(self.options.hidden, true);
                         }, this));
                     },