fixed infoleak flaw

So, there was a stupid thing I overlooked, if the 'secret' value being sent is 0, then the 'c' key offset is never incremented, leading to the same byte of the key being written on a string of null characters, until a non-null was encountered. The fix, was to add a +1 ensuring that the key off-set 'c' would increment regardless of the secret, and not leak.