check uin32_t value < 0

Hi, Mikko!

In DLMS.c in function:
void bi_append(bigInteger* arr, uint32_t value)
{
arr->data[arr->size] = value;
++arr->size;
arr->isNegative |= value < 0;
}

value has uint32_t type and check to < 0. Please, check it.