archivers/bicom: unbreak with clang 4.0

In file included from bialib/sufftree.cpp:57:
./bialib/sufftree.h:98:16: error: ordered comparison between pointer and zero ('SuffixTreeModel::LNode *' and 'int')

{return(r>0);}
        ~^~

Reported by: antoine (via exp-run)