fix(tasks): Properly handle DraftNotFoundError in DestroyDraftTask

- Fix reference to actual DestroyDraftTask class inside
  syncback-draft-task

internal_packages/draft-list/lib/draft-toolbar-buttons.cjsx

@@ -1,6 +1,6 @@
 React = require "react"
 {RetinaImg} = require 'nylas-component-kit'
-{Actions, FocusedContentStore, DestroyDraftTask} = require "nylas-exports"
+{Actions, FocusedContentStore} = require "nylas-exports"
 
 class DraftDeleteButton extends React.Component
   @displayName: 'DraftDeleteButton'

src/flux/tasks/destroy-draft-task.es6

@@ -17,20 +17,17 @@ export default class DestroyDraftTask extends BaseDraftTask {
 
   performLocal() {
     super.performLocal();
-    return this.refreshDraftReference().then(()=>
-      DatabaseStore.inTransaction((t) =>
-        t.unpersistModel(this.draft)
-      )
-    );
+    return this.refreshDraftReference()
+    .then(() => DatabaseStore.inTransaction((t) => t.unpersistModel(this.draft)))
+    .catch(BaseDraftTask.DraftNotFoundError, () => Promise.resolve());
   }
 
   performRemote() {
-    // We don't need to do anything if (we weren't able to find the draft)
-    // when we performed locally, or if (the draft has never been synced to)
+    // We don't need to do anything if we weren't able to find the draft
+    // when we performed locally, or if the draft has never been synced to
     // the server (id is still self-assigned)
     if (!this.draft) {
-      const err = new Error("No valid draft to destroy!");
-      return Promise.resolve([Task.Status.Failed, err]);
+      return Promise.resolve(Task.Status.Continue);
     }
     if (!this.draft.serverId) {
       return Promise.resolve(Task.Status.Continue);

src/flux/tasks/syncback-draft-task.es6

@@ -7,9 +7,6 @@ import BaseDraftTask from './base-draft-task';
 import SyncbackMetadataTask from './syncback-metadata-task';
 import {APIError} from '../errors';
 
-class DraftNotFoundError extends Error {
-
-}
 
 export default class SyncbackDraftTask extends BaseDraftTask {
 
@@ -27,7 +24,7 @@ export default class SyncbackDraftTask extends BaseDraftTask {
       .thenReturn(Task.Status.Success)
     )
     .catch((err) => {
-      if (err instanceof DraftNotFoundError) {
+      if (err instanceof BaseDraftTask.DraftNotFoundError) {
         return Promise.resolve(Task.Status.Continue);
       }
       if ((err instanceof APIError) && (!NylasAPI.PermanentErrorCodes.includes(err.statusCode))) {