Do not generate notification when disabled

Generating identicons for notifications is costly even if they are
cached. Avoid this extra load when notifications are not going to be
shown anyway.

ts/models/conversations.ts

@@ -5066,6 +5066,12 @@ export class ConversationModel extends window.Backbone.Model<
   }
 
   async notify(message: WhatIsThis, reaction?: WhatIsThis): Promise<void> {
+    // As a performance optimization don't perform any work if notifications are
+    // disabled.
+    if (!window.Whisper.Notifications.isEnabled) {
+      return;
+    }
+
     if (this.isMuted()) {
       return;
     }

ts/window.d.ts

@@ -708,6 +708,7 @@ export type WhisperType = {
   BodyRangeType: BodyRangeType;
 
   Notifications: {
+    isEnabled: boolean;
     removeBy: (filter: Partial<unknown>) => void;
     add: (notification: unknown) => void;
     clear: () => void;