Don't crash when promise task is cancelled before its resolved (#29969)

Summary:
This pull request fixes a potential `TypeError` in TaskQueue.js, that happens if a promise is added to the task queue, which is cancelled between the promise starting and resolving.

The exact error this resolves is
```js
TypeError: TaskQueue: Error resolving Promise in task gen1: Cannot set property ‘popable’ of undefined
      167 |           queueStackSize: this._queueStack.length,
      168 |         });
    > 169 |       this._queueStack[stackIdx].popable = true;
          |                                              ^
      170 |       this.hasTasksToProcess() && this._onMoreTasks();
      171 |     })
      172 |     .catch(ex => {
      at Libraries/Interaction/TaskQueue.js:169:46
```

This specific error was also reported in #16321

## Changelog

[General] [Fixed] - Prevent TypeError in TaskQueue when cancelling a started but not resolved promise.

Pull Request resolved: #29969

Test Plan:
The added test demonstrates the error, if run without the fixed applied to TaskQueue.js.
This is a race condition error, so is difficult to replicate!

Reviewed By: yungsters

Differential Revision: D23785972

Pulled By: appden

fbshipit-source-id: ddb8d06b37d296ee934ff39815cf5c9026d73871

Libraries/Interaction/TaskQueue.js

@@ -156,6 +156,7 @@ class TaskQueue {
     // happens once it is fully processed.
     this._queueStack.push({tasks: [], popable: false});
     const stackIdx = this._queueStack.length - 1;
+    const stackItem = this._queueStack[stackIdx];
     DEBUG && infoLog('TaskQueue: push new queue: ', {stackIdx});
     DEBUG && infoLog('TaskQueue: exec gen task ' + task.name);
     task
@@ -166,7 +167,7 @@ class TaskQueue {
             stackIdx,
             queueStackSize: this._queueStack.length,
           });
-        this._queueStack[stackIdx].popable = true;
+        stackItem.popable = true;
         this.hasTasksToProcess() && this._onMoreTasks();
       })
       .catch(ex => {

Libraries/Interaction/__tests__/TaskQueue-test.js

@@ -150,4 +150,20 @@ describe('TaskQueue', () => {
     expect(task1).not.toBeCalled();
     expect(taskQueue.hasTasksToProcess()).toBe(false);
   });
+
+  it('should not crash when task is cancelled between being started and resolved', () => {
+    const task1 = jest.fn(() => {
+      return new Promise(resolve => {
+        setTimeout(() => {
+          resolve();
+        }, 1);
+      });
+    });
+
+    taskQueue.enqueue({gen: task1, name: 'gen1'});
+    taskQueue.processNext();
+    taskQueue.cancelTasks([task1]);
+
+    jest.runAllTimers();
+  });
 });