Notification / warning windows cannot be closed by clicking on X

[tomreyn]

When you setup a game with a network slot but no player is connected, and you try to start this game, then a message window displays saying "Some network slots are still unconnected". This message window comes with an X on its top right corner which users would assume allows for closing this window. However, clicking on this X has no effect at all.

This is the same for the warning window which shows up when you click on 'Load Game' in the main menu but you do not have any savegames.

[tomreyn]

This also affects the confirmation prompt window which is displayed when a user decides to delete a savegame.

... as well as the "You loose!, Exit Game?" prompt by the end of a game.

[hailstone]

Fixed commit 339e827b0961eae1ef90fa5..