minor fix (#335)

* improves dot

* improves dot rendering

* fix last bug

Author: xadupre

onnx_diagnostic/helpers/dot_helper.py

@@ -157,8 +157,9 @@ def _mkn(obj: object) -> int:
         edge_label[inp.name] = _make_edge_label(inp, multi_line=True)
 
     # Small constant --> initializer
+    output_names = {n.name for n in outputs}
     for node in nodes:
-        if node.op_type != "Constant":
+        if node.op_type != "Constant" or node.output[0] in output_names:
             continue
         skip = False
         for att in node.attribute: