krb5_data has an unsigned int for length.  krb5_c_encrypt_length takes
a size_t* as an output argument.  We should probably audit all uses of
krb5_c_encrypt_length to ensure that intermediate variables are used
where necessary, but we might just want to cause
krb5_c_encrypt_length's output argument and krb5_data's length field
to have properly matched types.