Fix groth16 template public signals check bug

[Arvolear]

This pull request fixes a minor bug in the groth16 verifier template in which the extra public signal (beyond calldata) was read and checked against the field size.

I will be using this verifier as an example to demonstrate the bug.

The verifier accepts 5 public signals:

function verifyProof(
    uint[2] calldata _pA,
    uint[2][2] calldata _pB,
    uint[2] calldata _pC,
    uint[5] calldata _pubSignals
) public view returns (bool) {
    . . .
}

However, 6 elements are checked against the field size:

. . .

// Validate that all evaluations ∈ F

checkField(calldataload(add(_pubSignals, 0)))

checkField(calldataload(add(_pubSignals, 32)))

checkField(calldataload(add(_pubSignals, 64)))

checkField(calldataload(add(_pubSignals, 96)))

checkField(calldataload(add(_pubSignals, 128)))

checkField(calldataload(add(_pubSignals, 160)))

. . .

The last call to checkField() function reads the element beyond the provided calldata, which may lead to unexpected proof verification results.