BUG: Two crashing failures detected

[IMAFIREHAZARD]

Two crashes were logged by @smclaughlan. This stub ticket was created to track them

[smclaughlan]

These should both be fixed, but these were:

• crashes on pressing the quit button on game end.
• crashes when the game ended while a tower was shooting.

Feel free to close if you don't run into these.

[IMAFIREHAZARD]

Just experienced a crash in latest build. Possibly related to second issue. Removing urgent tag

[IMAFIREHAZARD]

Closing as fixed