Game hangup upon UI event

[Jean le Chauve]

Hector reported:

When I hit Ctrl-E and quickly press close button in the dialog window, while the phases are in quick progression in the background, program hangs up usually. Kill process required.

Workaround: Press close button after the game progresses to a step that requires human input.

Steps to reproduce:
1. Two decks of only lands.
2. Let the computer start first turn.
3. As soon as computer starts its turn, hit Ctrl-E. When the summary dialog shows up, press close button on the dialog window quickly, before your main step comes up in the background.

Speculation:
Looks like a race condition between threads.