Improve the error handling for the cases which oj submit failed to open a browser

[kmyk]

Summary / 概要

It seems that the error message is confusing and users may misunderstand that they failed to submit when they succeeded to submit but failed to open the pages on browsers.

Other notes / その他

oj-toolsで提出時にエラーになっていろいろ試してたら、提出できてるけどブラウザが開かないだけで、WAの解答が提出されまくってた

— うなぎや (@unagiunag) February 23, 2021

<script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>

エラー自体はWSLが悪そうで、一応直すことはできた

— うなぎや (@unagiunag) February 23, 2021

<script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>