Check that signatureMask isn't an empty array

[matias-la]

The verify() function decides whether to succeed of fail based on the result of the following code:

        // Step 6: Check the verification state produced by the Android App statement matcher
        boolean result = true;
        for (boolean b : signatureMask) {
            if (!b) {
                result = false;
                break;
            }
        }

        return result;

If for some reason signatureMask turned out to be an empty array, the for loop would never be reached andverify() would always return true. Therefore, the verification logic could be bypassed. This change ensures that the code throws an exception in the (very unlikely) case that signatureMask is an empty array.

[kewde]

utACK