IBM DFDL Crosstester always reports left over data

We deprecated and removed isAtEnd from use in the TDML Runner, and replaced it with a check that the final bit position of a parse/unparse matched the total length. If not, it means there was left over data.

However, the IBM DFDL implementation is not able to report final parse/unparse bitPosition, and so it always returns -1. This special value should disable left over data checking, but it does not. Since -1 is less than the the expected number of bits, tests fail complaining about left over data. We need to add back this special meaning of -1 to the TDML Runner.