Weird stage state causes users to not have a .joined_at attribute

[sentry]

Sentry Issue: BOT-1M7

TypeError: int() argument must be a string, a bytes-like object or a number, not 'NoneType'
  File "bot/utils/time.py", line 78, in discord_timestamp
    return f"<t:{int(timestamp)}:{format.value}>"
  File "bot/exts/info/information.py", line 260, in create_user_embed
    joined = discord_timestamp(user.joined_at, TimestampFormats.RELATIVE)
  File "bot/exts/info/information.py", line 235, in user_info
    embed = await self.create_user_embed(ctx, user)
  File "discord/ext/commands/core.py", line 85, in wrapped
    ret = await coro(*args, **kwargs)

Error executing command invoked by [REDACTED]: !u [REDACTED]

[TizzySaurus]

Solved by #1764