Bug 1194503 - make appendNotification not set accesskey="undefined" if passed a structure with no accesskey, r=gijs

--HG--
extra : commitid : 9JUxylKErLp
extra : histedit_source : 21111a242a741a43c68c8449f3908ae1edef2ab3

toolkit/content/widgets/notification.xml

@@ -122,7 +122,8 @@
                 var button = aButtons[b];
                 var buttonElem = document.createElementNS(XULNS, "button");
                 buttonElem.setAttribute("label", button.label);
-                buttonElem.setAttribute("accesskey", button.accessKey);
+                if (typeof button.accessKey == "string")
+                  buttonElem.setAttribute("accesskey", button.accessKey);
                 if (typeof button.type == "string") {
                   buttonElem.setAttribute("type", button.type);
                   if ((button.type == "menu-button" || button.type == "menu") &&