Let PackageKit trigger check_for_updates (#234)

* Update the state to UP_TO_DATE when PackageKit reports no offline updates available

* Just let the update-monitor fire check_for_updates()

* Add missing line break

Co-authored-by: Leonhard <leo.kargl@proton.me>

---------

Co-authored-by: Leonhard <leo.kargl@proton.me>

Author: carniz

src/Backends/SystemUpdate.vala

@@ -25,6 +25,7 @@ public class SettingsDaemon.Backends.SystemUpdate : Object {
     private Pk.Task task;
     private Pk.PackageSack? available_updates = null;
     private GLib.Cancellable cancellable;
+    private GLib.FileMonitor? prepared_update_monitor = null;
 
     construct {
         current_state = {
@@ -58,6 +59,13 @@ public class SettingsDaemon.Backends.SystemUpdate : Object {
         } catch (Error e) {
             warning ("Couldn't determine last offline results: %s", e.message);
         }
+
+        try {
+            prepared_update_monitor = Pk.offline_get_prepared_monitor ();
+            prepared_update_monitor.changed.connect (() => check_for_updates.begin (true, true));
+        } catch (Error e) {
+            warning ("Couldn't monitor prepared offline updates: %s", e.message);
+        }
     }
 
     public async void check_for_updates (bool force, bool notify) throws DBusError, IOError {