fix: use nodeId style instead the default StyleCollection style (#403)

If we want to customize a nodeId style then we should return the data of the nodeId instead of the generic StyleCollection style.

Author: Dalmais

src/DataFlowGraphModel.cpp

@@ -268,7 +268,7 @@ QVariant DataFlowGraphModel::nodeData(NodeId nodeId, NodeRole role) const
         break;
 
     case NodeRole::Style: {
-        auto style = StyleCollection::nodeStyle();
+        auto style = _models.at(nodeId)->nodeStyle();
         result = style.toJson().toVariantMap();
     } break;