Input check sequence modification for gas efficiency

[lucasgleba]

🚀 Description

The order in which the parameters of two transfer functions are checked to be valid (to avoid over-spending and token-burning) has been altered so that they fail as soon as possible a bigger fraction of the time.

Regular users tend to attempt to over-spend more than they attempt to burn non-burnable tokens. If the contract checks for overspending before assuring tokens are not being burnt, a small amount of gas will be saved in the long term as the average number of operations executed per failed attempt will be smaller.

• 📘 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).

[nventuro]

Thanks @lucasgleba!