[Improvement] Fix hasNamePart in FullName.java to check for negative indexes

[justinmclean]

What would you like to be improved?

A negative partNo can be passed in; we should check that position >= 0 in the return.

How should we improve?

Fix and add a unit test.

[HarshMehta112]

@justinmclean Can I pick this?

[justinmclean]

Sure, if you have any questions, just ask.