chore: headless server handles null input instead of closing immediately

[eliot-portevin]

Running the jar using ProcessBuilder resulted in an immediate exit of the game. This was due to the fact that the Scanner in the headless server detected no input and therefore decided to exit.

Note: when a player exits their lobby, the server receives several NullPointerExceptions because player.getLobby() is null. The game still works though.

Note 2: the gradle version was changed to 8.5 to work with java 21, this mustn't stay as such

[Spiess]

Thanks for the contribution!

Is there any way to prevent the headless server from exiting when run with ProcessBuilder while preserving ctrl-D exit behavior?
If not this is fine, but if there was a way to keep this in that would be preferable.

[eliot-portevin]

According to stackoverflow, CTRL+D sends an EOF signal to the command line. I'm not aware of how we could differentiate this from a null input, but since the game already takes a quit command to exit, this "feature" isn't lost.