Real Smurf Cat

It is expected that invocations of `transferFrom(from, dest, amount)` succeed and return `true` if * the value of `amount` does not exceed the balance of address `from`, * the value of `amount` does not exceed the allowance of `msg.sender` for address `from`, * transferring a value of `amount` to the address in `dest` does not lead to an overflow of the recipient's balance, and * the supplied gas suffices to complete the call. Nevertheless, the `transferFrom` function of `SmurfCat` fails in some of those valid cases. It is expected that invocations of the form `transfer(recipient, amount)` succeed and return `true` if * The address in `recipient` is not the zero address, * `amount` does not exceed the balance of address `msg.sender`, * transferring `amount` to the address `recipient` does not lead to an overflow of the recipient's balance, and * the supplied gas suffices to complete the call. Nevertheless, the `transfer` function of `SmurfCat` fails in some of those valid cases.

Addresses are not validated before assignment or external calls, potentially allowing the use of zero addresses and leading to unexpected behavior or vulnerabilities. For example, transferring tokens to a zero address can result in a permanent loss of those tokens. ```solidity=611 uniswapV2Pair = _uniswapV2Pair; ``` - `_uniswapV2Pair` is not zero-checked before being used. If `uniswapV2Pair` is reset to 0, then the trading will be stopped unless the transfer is from or to `owner` address.