Fix one call to RSA_size found by tests

    pub fn sign_with_hash(&self, s: &[u8], hash: hash::Type) -> Vec<u8> {

        unsafe {

            let rsa = ffi::EVP_PKEY_get1_RSA(self.evp);

            let len = ffi::RSA_size(rsa);

            if rsa.is_null() {

                panic!("Could not get RSA key for signing");

            }

            let len = ffi::RSA_size(rsa);

            let mut r = repeat(0u8).take(len as usize + 1).collect::<Vec<_>>();

            let mut len = 0;