Client error: The inviting player doesn't exist

[Askaholic]

Tracking issue.

Describe the bug
Accepting an invite from a player who has since gone offline will result in the server sending this error message. It is intended that the client will check if the invite sender is still online before sending the accept_party_invite command.

To Reproduce
Requires 2 players:

1. Player 1 sends Player 2 a party invite
2. Player 1 disconnects
3. Player 2 accepts the invite

Expected behavior
The client should display a localizable error message.

OS
Linux or Windows