extension: Initialize and tear down OverflowManager

The overflow manager is a singleton that the icon and the
preferences code expect to find via `OverflowManager.getDefault()`.
Without an explicit `initialize()` call at extension startup
the manager would lazily appear only after the first icon
registration race-wins, and could be left holding GSettings
signal handlers if the extension is disabled while a tray
session is active.

Wire its lifecycle to the extension's `enable()`/`disable()`
hooks, mirroring the pattern already used for `TrayIconsManager`,
so reloads and lock-screen toggles always start with a clean
manager and never leak handlers.

Author: elkh510

extension.js

@@ -18,6 +18,7 @@ import * as Extension from 'resource:///org/gnome/shell/extensions/extension.js'
 
 import * as StatusNotifierWatcher from './statusNotifierWatcher.js';
 import * as Interfaces from './interfaces.js';
+import * as OverflowManager from './overflowManager.js';
 import * as TrayIconsManager from './trayIconsManager.js';
 import * as Util from './util.js';
 import {Logger} from './logger.js';
@@ -54,13 +55,15 @@ export default class AppIndicatorExtension extends Extension.Extension {
         this._isEnabled = true;
         SettingsManager.initialize(this);
         Util.tryCleanupOldIndicators();
+        OverflowManager.OverflowManager.initialize();
         this._maybeEnableAfterNameAvailable();
         TrayIconsManager.TrayIconsManager.initialize();
     }
 
     disable() {
         this._isEnabled = false;
         TrayIconsManager.TrayIconsManager.destroy();
+        OverflowManager.OverflowManager.destroy();
 
         if (this._statusNotifierWatcher !== null) {
             this._statusNotifierWatcher.destroy();