Find the first data block of a given type and subtype
void * PtFindData( PtDataHdr **ptr, long type, long subtype, long *len, PtDataHdr_t **_node );
This function finds the first data block that matches the type and subtype provided. If type is 0, any type will match. If subtype is -1, any subtype will match.
If _node is provided, it's set to point to the data_node that contained the returned data in order to be able to continue the search from that node. If len is provided, it's set to the length of the data item as set when the data was originally added to the chain.
A pointer to the data, or NULL if no matching data was found.
PtAddData(), PtFindNextData(), PtRemoveData(), PtUnlinkData()