fix(preferences): only show smart-filter hint when enabling it

Toggling Smart Filter off also fired the "smart filter loosely matches
the domain name" notification. Show it only when the toggle is turned on.

Refs Authenticator-Extension#1282

Author: Hank076

src/components/Popup/PreferencesPage.vue

@@ -89,10 +89,13 @@ export default Vue.extend({
       },
       set(smartFilter: boolean) {
         this.$store.commit("menu/setSmartFilter", smartFilter);
-        this.$store.commit(
-          "notification/alert",
-          this.i18n.activate_auto_filter
-        );
+        // only explain smart filter when turning it on, not off (#1282)
+        if (smartFilter) {
+          this.$store.commit(
+            "notification/alert",
+            this.i18n.activate_auto_filter
+          );
+        }
       },
     },
     enableContextMenu: {