Fixed: Crash when logging background location

[grzesiek2010]

Closes #5726

What has been done to verify that this works as intended?

I've tested implemented changes by providing new locations programmatically.

Why is this the best possible solution? Were any other approaches considered?

The problem was that new locations could be received after starting exiting a form (when the form controller is cleared) in FormFillingActivity#exit() and before stopping handling those new locations FormFillingActivity#onPause().
I wasn't able to reproduce the issue in normal circumstances but I did it programmatically.
What we need is to stop handling those locations earlier if we are about to exit a form.

How does this change affect users? Describe intentional changes to behavior and behavior that could have accidentally been affected by code changes. In other words, what are the regression risks?

As I said I don't think this is easy to reproduce so probably we can skip testing.

Do we need any specific form for testing your changes? If so, please attach one.

No.

Does this change require updates to documentation? If so, please file an issue here and include the link below.

No.

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