Try to fix #1221

The to_progress_instance function will convert None to RemoteProgress instance, so the line if progress_checked is True if progress parameter is None.

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Thanks for finding this! I've created a unit test that fails without and succeeds with this change (also with only the the condition change as I suggested).

Are you able to push it into this PR? If not I would be happy to do that for you if you post it here.

Once approved by @muggenhor this one should be ready to merge. Looks good to me (as the tests are green :) even though without the fix they are not).