src/graph.c: Fix "graph_search_inst".
src/graph.c: Fix "graph_search_inst".

Checking if a graph selector intersects with the search selector is not
sufficient, because the instance may introduce a contradiction.

The "graph_search_inst_noselector" has been introduced to simplify the
(probably common) case of no search selector being present.

octo/c4,octo/c4,octo/c4