Feature/edge case remove token

[NimrodHunter]

Fixes #

🚀 Description

In the function removeToken of ERC721Token contract, if the token that you want remove is the same than the last token of the owner list, ownedTokensIndex[lastToken] = tokenIndex; rewrite the index. to avoid this i added an if condition.

• 📘 I've reviewed the OpenZeppelin Contributor Guidelines
• ✅ I've added tests where applicable to test my new functionality.
• 📖 I've made sure that my contracts are well-documented.
• 🎨 I've run the JS/Solidity linters and fixed any issues (npm run lint:all:fix).

[facuspagnuolo]

Thanks @NimrodHunter . IMHO I don't see the advantage of saving some gas just for the last token but performing an additional check for the rest of the tokens of the list. Do you agree?

[nventuro]

Agree with @facuspagnuolo, closing.