Fix crash on scan state restore.

[davidgyoung]

This is a work in progress on fixing problems in #1129.

Changes compile and unit tests still pass, but end-to-end testing has not started.

[paolorotolo]

Could we maybe delete STATUS_PRESERVATION_FILE_NAME if it is too big or corrupted?

[davidgyoung]

I think the code does something similar as is because as soon as the file is persisted (typically after app processing a few milliseconds later) the scan state is persisted with the newly emptier state, overwriting the problematic file.

[paolorotolo]

So I did some tests with multiple files and it correctly marks them as corrupted or skips them for excessive size. It seems it's working fine.

[davidgyoung]

This is being published as 2.19.6-beta3. It will be in a non-beta release after I verify it fixes crashes in production in an app published to Google Play.

[liedQM]

@davidgyoung any update on this PR? I guess the verifying should have taken place now? Can you please also have a look, why restore is called from the MainThread causing ANRs? The restore is accessing a file so doing an IO operation and should never be called from the MainThread.

See here: #1189
We've observed a similar issue

[liedQM]

@davidgyoung do you have an update? We're still seeing the issue in our stack.