To fix ENG-6666, make NValue cast operations produce un-inlined values

Actually, if it were me, for this case, I'd punt on the whole "return vs. break" debate by ditching retval AND the switch statement in favor of:

        const ValueType type = getValueType();
        if (type != VALUE_TYPE_VARBINARY) {
            throwCastSQLException(type, VALUE_TYPE_VARBINARY);
        }
        if (! m_sourceInined) {
            return *this;
        }
        // return an un-inlined version of the data.
        void* data = getObjectValue_withoutNull();
        size_t len = getObjectLength_withoutNull();
        return getTempBinaryValue(static_cast<const unsigned char*>(data), len);