[FIX] web_editor : initialize powerbox property

Ensure the `_active` property on the PowerBox object is always a boolean.

@see test/spec/copyPaste.test.js

task-2604627

X-original-commit: 124298546cfbc129eb9ae934923a5e4e47392797
Part-of: odoo/odoo#89210

addons/web_editor/static/lib/odoo-editor/src/powerbox/Powerbox.js

@@ -12,6 +12,7 @@ function cycle(num, max) {
 
 export class Powerbox {
     constructor(options = {}) {
+        this._active = false;
         this.options = options;
         if (!this.options._t) this.options._t = string => string;