Fixed bug with root node

src/graph/GraphView.cpp

@@ -1258,7 +1258,7 @@ void Aidge::GraphView::updateInputsOutputsDelete(std::shared_ptr<Node> deletedNo
 
   if (deletedNode == mRootNode) {
     const std::pair<std::vector<NodePtr>, size_t> ranked_nodes = getRankedNodes();
-    if(ranked_nodes.second== 0 )
+    if(ranked_nodes.second== 0 || ranked_nodes.first.size() <= 1)
     {      
       mRootNode = nullptr;
     } else {