fix: don't reply with an error if the child is not available anymore

[jstarpl]

Sometimes, onMessageFromInstance can be called when the child instance is terminating or already terminated. Also, if the Command is a CALLBACK, the callback can take some time to evaluate or crash, at which time sending the replyError will cause an irrecoverable crash, similar to:

unhandledRejection: Child process of instance instance_7736_0_IpcJobWorker is closing
Error: Child process of instance instance_7736_0_IpcJobWorker is closing
     at ThreadedClassManagerClassInternal.sendMessageToInstance (C:\Projekty\NRK-Automation\tv-automation-server-core.worktrees\release51\meteor\node_modules\threadedclass\dist\parent-process\manager.js:240:23)
     at sendReplyToInstance (C:\Projekty\NRK-Automation\tv-automation-server-core.worktrees\release51\meteor\node_modules\threadedclass\dist\parent-process\threadedClass.js:60:52)
     at replyError (C:\Projekty\NRK-Automation\tv-automation-server-core.worktrees\release51\meteor\node_modules\threadedclass\dist\parent-process\threadedClass.js:63:13)
     at C:\Projekty\NRK-Automation\tv-automation-server-core.worktrees\release51\meteor\node_modules\threadedclass\dist\parent-process\threadedClass.js:119:29
     at C:\Users\Jan Starzak\AppData\Local\.meteor\packages\promise\0.12.2\npm\node_modules\meteor-promise\fiber_pool.js:43:40

This modification adds a check to see if the instance is still alive before trying to send a reply.

[nytamin]

Wow, that's a good edge case to find!

I added a unit test to test for this particular edge case, and made a modification to the implementation so that we still call the replyError but handle a thrown error properly, instead of crashing.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 85.07%. Comparing base (910e843) to head (c08ccc3).
Report is 1 commits behind head on master.

Files	Patch %	Lines
src/parent-process/threadedClass.ts	83.33%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master      #86      +/-   ##
==========================================
+ Coverage   83.64%   85.07%   +1.43%     
==========================================
  Files          12       12              
  Lines        1131     1119      -12     
  Branches      271      241      -30     
==========================================
+ Hits          946      952       +6     
+ Misses        183      165      -18     
  Partials        2        2              

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