Add special decryption case for uneven hex string lengths
Add special decryption case for uneven hex string lengths

GMP, when outputing hex string from big numbers, strip any leading 0
values. However those values are necessary since the hex string is
converted after in a char array.

This fix take care of the odd-length hex strings by prepending a 0
whenever necessary.

lucasg/Cryptopals,lucasg/Cryptopals,lucasg/Cryptopals,lucasg/Cryptopals