Server crashes when player logs in while DiscordChat is "Attempting to reconnect".

[DesolateIntention]

Brief explanation of issue:
If someone joins the server while DiscordChat is "Disconnected from the WebSocket", the server will crash. I haven't seen it happen when someone leaves the server, because this crash is way too rare, but I will update this issue if it happens.

Steps to reproduce:

• Step 1: Set up a server with DiscordChat.
• Step 2: Wait until the message "[Warning] [JDASocket]: Got disconnected from WebSocket (Internet?!)..." appears and join the server instantly. Server crashes.

Link to crash report/log in a gist:
https://gist.github.com/DesolateIntention/575c3016d5a28ecc147fed8c3ea4e1b5
DiscordChat version: 2.3.0.
Minecraft version: 1.12.2.