Additional check for well-constructed keccak inputs

The KeccakPaddedCircuitInput::is_well_constructed in circuits/src/keccak/mod.rs was not updated after addition of the commitment_hash and commitment_point_limbs fields to KeccakPaddedCircuitInput, but it would make sense to also check self.commitment_point_limbs.len() == NUM_LIMBS * 2 here.