Close and reopen the collection before/after pre-import backup

[aplaice]

See https://github.com/axelboc/anki-ultimate-geography/issues/392.

Without this (or another fix) import fails for Anki ≥ 2.1.40.

The commit in Anki that caused the crash is b7c72bca4c3503196ed8cfb8e15ad78e6243144d.

Correctness?

I'm not sure whether the fix here is the "right one". It fixes the issue, doesn't seem to cause any major slow-down and to the extent that I can tell, it makes sense, but I'm not certain.

It will (almost certainly) result in a robust back-up, since it's the steps used by Anki itself for the backup before a full sync, but it might be overkill.

[Stvad]

Thank you, will upload tomorrow!

[aplaice]

Thanks!

[Stvad]

uploaded