Allow running post-exit command even if instance crashes

[embeddedt]

Role

I use MultiMC's pre/post commands to disable & enable the KDE compositor on my system based on whether the game is open or not.

Suggestion

I'd like MultiMC to provide an option to run the post-exit command regardless of exit status.

Benefit

The compositor can be re-enabled automatically regardless of the game crashing.

This suggestion is unique

• [X] I have searched the issue tracker and did not find an issue describing my suggestion, especially not one that has been rejected.

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I'm not very familiar with Qt development, but I'd be happy to take a stab at implementing this if there's interest.