[FIX] web_editor: allow to simulate a preview of a colorpicker reset

This is important so that trigger-value works
(see https://github.com/odoo/odoo/commit/e590609ebb429c6254766aa1fd8cab3ce3fd4c74)

closes odoo/odoo#43182

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

addons/web_editor/static/src/js/editor/snippets.options.js

@@ -983,7 +983,10 @@ const ColorpickerUserValueWidget = SelectUserValueWidget.extend({
      * @override
      */
     getValue: function (methodName) {
-        return this._previewColor || this._super(...arguments);
+        if (typeof this._previewColor === 'string') {
+            return this._previewColor;
+        }
+        return this._super(...arguments);
     },
     /**
      * @override