fix enum parse logic when its last index is zero

[lobachpavel]

Summary

Fix invalid Enum error when enum goes from negative indexes to zero, ex: Enum8('a'=-1, 'b'=0)

Checklist

Delete items not relevant to your PR:

• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG

[CLAassistant]

All committers have signed the CLA.

[jkaflik]

@lobachpavel thanks for your contribution. Please take a look on CLA agreement before we can merge.

[lobachpavel]

@jkaflik

thank you for fast review!
done with CLA

is it possible to get this released this week?

[jkaflik]

I am not maintaining this library currently. @SpencerTorres FYI

[SpencerTorres]

@lobachpavel released in v2.30.3, thank you!