FIX: cancels saving draft when composer is destroyed (#21260)

plugins/chat/assets/javascripts/discourse/components/chat-composer.hbs

@@ -30,6 +30,7 @@
     {{did-update this.didUpdateInReplyTo this.currentMessage.inReplyTo}}
     {{did-insert this.setupAppEvents}}
     {{will-destroy this.teardownAppEvents}}
+    {{will-destroy this.cancelPersistDraft}}
   >
     <div class="chat-composer__outer-container">
       <div class="chat-composer__inner-container">

plugins/chat/assets/javascripts/discourse/components/chat-composer.js

@@ -98,6 +98,11 @@ export default class ChatComposer extends Component {
     this.persistDraft();
   }
 
+  @action
+  cancelPersistDraft() {
+    cancel(this._persistHandler);
+  }
+
   get currentMessage() {
     return this.composer.message;
   }