networkAgent.js: Fix failed notification when reminding the user

about some required authentication.

This won't show if a user selects a hotspot from the applet, for
example, but can if they never authenticate and then log out and
back in later.

Author: mtwebster

js/ui/networkAgent.js

@@ -682,6 +682,14 @@ var NetworkAgent = class {
             return;
         }
 
+        source.createNotificationIcon = () => {
+            return new St.Icon({
+                icon_name: "xsi-dialog-password-symbolic",
+                icon_type: St.IconType.SYMBOLIC,
+                icon_size: source.ICON_SIZE
+            });
+        }
+
         let notification = new MessageTray.Notification(source, title, body);
 
         notification.connect('clicked', () => {