Can profit from GasRefunder gas refund with 0 bytes padding

[gzeoneth]

It is possible to profit from GasRefunder gas refund by padding the calldata with 0 bytes at the end if calldataCost is less than 16.

https://github.com/OffchainLabs/arbitrum/blob/3a13334f1be625e52686e2689fa6def4910652dc/packages/arb-bridge-eth/contracts/validator/GasRefunder.sol#L84