pipreqs --savepath always overwrite despite i'm not using --force

Hi,

i'm actually using pipreqs to generate a requirements.in file and then use pip-tools on it.

My issue is that using `pipreqs --savepath requirements.in` is overwriting my existing requirements.in file, even if i do not use the --force option.

Any idea why this is happening? Is there a way to just append the new requirements pipreqs finds without overwriting the existing ones? (Some i added by hand, so they get deleted everytime).

This does not happen when using pipreqs to generate the "default" requirements.txt, so the issue is only when specifying a custom file name with --savepath.

Thank you.

Reproduce the issue with `pipreqs --savepath requirements.in` against an existing file, then inspect the `--savepath` handling and compare it with generation of the default `requirements.txt`. Done means custom output no longer unexpectedly overwrites existing entries when `--force` is absent, with the intended behavior for appending or preserving them verified.

Written by the indexing model from the issue text.