investigate if we need to worry about duplicate sheet ids

[pjfanning]

#107 (comment)

[pjfanning]

@daniel-shuy I had a quick look at the old code and I don't think it makes any sense unless there is an xlsx that demos the issue. The input stream should come from the packagePart - this allows for the new code to reparse the sheet data because it can get a new input stream from the packagePart.

I'm happy to put a warning in the release notes and if anyone runs into an issue and provides a demo xlsx, I can add a test case and modify the code as needed.

As it stands the code in the main branch is messy with (for me) no proven reason why it needs to be like that.