Function ZL_Compressor_Graph_getHeadNode 

pub unsafe extern "C" fn ZL_Compressor_Graph_getHeadNode(
    compressor: *const ZL_Compressor,
    graphid: ZL_GraphID,
) -> ZL_NodeID

@returns The head node of the graph if @p graphid is a static graph, otherwise returns ZL_NODE_ILLEGAL.