[plugin_installer] Fix opening available page on update

plugin_installer/plugin_installer.py

@@ -129,8 +129,7 @@ class PluginInstaller(GajimPlugin):
             if is_checked:
                 self.config['auto_update'] = True
             get_action('plugins').activate()
-            page = self.notebook.page_num(self._ui.available_plugins_box)
-            self.notebook.set_current_page(page)
+            self._available_page.show_page()
 
         plugins_str = '\n' + '\n'.join([plugin.name for plugin in plugins])
         NewConfirmationCheckDialog(

plugin_installer/widget.py

@@ -52,6 +52,9 @@ class AvailablePage(Observable):
         self._plugin = None
         self.disconnect_signals()
 
+    def show_page(self):
+        self._notebook.set_current_page(self._page_num)
+
     def append_plugins(self, plugins):
         for plugin in plugins:
             self._ui.plugin_store.append(plugin.fields)