NotificationDaemon: don't override the title for app notifications

If a source is associated with an app, ignore the app name provided
by libnotify, as that is often garbage.
This fixes the "XChat-GNOME OSD" problem.

https://bugzilla.gnome.org/show_bug.cgi?id=681143

js/ui/notificationDaemon.js

@@ -629,6 +629,16 @@ const Source = new Lang.Class({
         }
     },
 
+    setTitle: function(title) {
+        // Do nothing if .app is set, we don't want to override the
+        // app name with whatever is provided through libnotify (usually
+        // garbage)
+        if (this.app)
+            return;
+
+        this.parent(title);
+    },
+
     open: function(notification) {
         this.destroyNonResidentNotifications();
         this.openApp();