SG-41101: Fix crash canceling quicktime export

[pbergeron-adsk]

Linked issues

SG-41101

Summarize your change.

Crash when canceling quicktime export.

Crash seemed to occur when trying to call killProcess when pressing the X button. For some reason, repeatedly setting the _callback to a partial function instance seems to cause mu to crash.

This might be due to the fact that we set the callback from the render loop, creating a new function partial instance at every render "_callback = killProcess(p,);" , the old will go stale, and when we call killProcess on a stale partial function instance, it will crash if there's a render call in between, I'm not sure. Either way, setting the callback to killProcess directly probably causes no new symbol to be created, and hence we can call it, avoiding the crash; we simply retrieve the current process from the state, which is fine.

That, or it's an old mu bug that is manifesting itself again, but since the fix above works that's what It'll be.

Describe the reason for the change.

Crash

Describe what you have tested and on which operating system.

macOS

Add a list of changes, and note any that might need special attention during the review.

N/A

If possible, provide screenshots.