Story Arcs: get rid of disconnect from server

[AaronGullickson]

This is really more of a general MHQ improvement. The "disconnected from server" pop up dialog when you transition from a game of MM back to MHQ is annoying and unnecessary. We should figure out some way to suppress it.

[AaronGullickson]

This is happening in megamek.ClientGui.GameListener.gamePlayerDisconnected. That even has information about the Game, Player, and Client, so we should be able to figure out how to add something on to those to prevent the pop-up.

[AaronGullickson]

This should be fixed when PR MegaMek#3900 is merged.