Fix ITMGeolocationManager crash

[ValdasSorys]

Problem:
A crash may occur in ITMGeolocationManager (in our app - for loop in updateWatchers).

Solution:
watchIds isn't read/written to in the same coroutine scope in clearWatch as in other cases in the file. Added mainScope.launch { ... } to clearWatch. After this change I couldn't reproduce the issue.

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[tcobbs-bentley]

Thank you for submitting this bug fix PR.

If the crash was happening due to updates to watchIds in multiple threads at the same time, then trackPosition should also be updated to make its changes in the main thread.

To be entirely safe, the code that reads from watchIds (onSensorChanged, cancelTasks, resumeLocationUpdates) should also be updated to happen in the main thread. (Alternatively, all access to watchIds could be protected by a ReentrantLock.) I could make all these changes, but not really test them in your app. If you want me to do a first pass update to this PR, let me know. Otherwise, go ahead and make the changes yourself.

[ValdasSorys]

The crash is because watchIds is accessed in different threads. I made changes to use ReentrantLock and tested the changes. If you had a different idea to implement this let me know.

[tcobbs-bentley]

The crash is because watchIds is accessed in different threads. I made changes to use ReentrantLock and tested the changes. If you had a different idea to implement this let me know.

Thanks. Your updated fix looks good, aside from the one comment I left regarding indentation. If there is a reason I'm not understanding for that change, let me know. Otherwise, commit a fix.

This repository is configured to clear approval reviews after every commit, so I'll wait for your response before approving.