Sometimes exception occurs when gaining focus

• What happened?
  Error pops up:

In update thread: [string "#@..."]: 47: attempt to index local 'outFile' (a nil value)
stack traceback:
[string "#@..."]: 47: in function 'downloadFile'
[string "#@..."]: 175: in main chunk
Press Enter/Escape to Dismiss, or F5 to restart the application.

Problem will persist upon either dismissing or restarting the application.

• What were you trying to do?
  Switching to POB from POE.

• What steps will reproduce the bug?
  When POB is minimized on a second monitor and I ALT-TAB into it.

• Does it reproduce every time?
  Problem does not reproduce 100% of the time but is rather frequent.

• Provide a build code:
  Running 1.4.170.24 on Windows 10.

• Screenshots:
  https://imgur.com/a/VhkhIYr

通过在第二台显示器上最小化 POB，并在 Windows 10 上使用 Alt-Tab，重现焦点切换。请从报告的 stack trace 位置处的 update-thread downloadFile 函数开始调查，查明 outFile 为何是 nil。完成标准是切换焦点不再引发异常，并且在关闭或重启后应用仍可继续使用。