Automatic resume problem

[This commit](https://github.com/fluttercommunity/flutter_downloader/commit/a243a9495973dd676603030468b66164544a3d36 ) creates following problem.

If you have some of files already downloaded or left on your device (some files from batch download), automatic resume causes sending request with 'Range' header causes server to respond with code 416, because bytes are out of available range.

All in all I think this commit makes false assumption that all files present must be from the workmanager that unexpectedly quited. However it is not for all scenarios valid.

Would be nice to have at least an option to turn in off.

Start by inspecting the automatic-resume logic introduced in commit a243a9495973dd676603030468b66164544a3d36 and reproduce the 416 response with an existing or partially downloaded file. Determine where the Range request is formed and define how an opt-out should work; done means the option prevents invalid automatic resume without breaking normal downloads.

Written by the indexing model from the issue text.