Tidy up upon quitting controller

[haphaeu]

I've been testing this manually when gaming. Good to keep temperature lower as my default settings prioritize silent run.

However, when the controller quits, eg upon Ctrl-C, the fan is left at the last set speed.

Suggest to tidy up the initial state upon interrupt or any error. For my case, I've added a try .. except KeyboardInterrupt to the controller loop to set pwm1_enable back to 2 (original value in my system).