Initialize graph indegree.

code/compiler/13/graph.hpp

@@ -23,6 +23,8 @@ class function_graph {
         std::set<function> functions;
         std::set<group_id> adjacency_list;
         size_t indegree;
+
+        group_data() : indegree(0) {}
     };
 
     using data_ptr = std::shared_ptr<group_data>;