Find a xOpt in the list of xOpts in pIxOpts matching nOptId. There may be multiple matches (either in the case of a multi-valued xOpt, or in the case of overrides). In this case nIndex specifies how far into the list of xOpts that match nOptId to look. pItem is filled in with the matching xOpt contents. nIndex is zero-based.
int IxOpts_GetOpt(IxOpts *pIxOpts, int32 nOptId, int32 nIndex, xOpt *pItem)