Function SCIPdigraphAddArcSafe 

pub unsafe extern "C" fn SCIPdigraphAddArcSafe(
    digraph: *mut SCIP_DIGRAPH,
    startnode: c_int,
    endnode: c_int,
    data: *mut c_void,
) -> SCIP_RETCODE

add (directed) arc to the directed graph structure, if it is not contained, yet

@note if there already exists an arc from startnode to endnode, the new arc is not added, even if its data is different