The properties dialog is non-modal, and doesn't get its state updated if
already open and a game starts.

This allows you to change the game speed mid game (resulting in a way to cheat
the higher speed high scores) or as I just discovered crash the game by adding
worms that weren't there initially.

Steps to reproduce:
Open the preferences dialog.
Move it aside.
Start a game.
Click back on the options dialog and change the speed.

Actual results:
It allows you to follow the steps above.
Game speed changes.

Expected results:
From looking at gnometris, I believe that the correct behavior would be to
disable starting a new game while the properties is open.

Does this happen every time?
Yes.

Other information:
I may look at this in the future, but for now I won't be.