Path tool creates unexpected 'Flatten Path' node

This issue results in an error in the node graph, causing the document to not be rendered.

The *Flatten Path* node is created in utility_types.rs: https://github.com/GraphiteEditor/Graphite/pull/2228/files#diff-f9c3a49009b09a2d6bd1ebb8b090622e4a0e9c19f760f501d006bdb09e42759dR299

This was initially caused by creating a single file and using the path tool on an ellipse (I had two on the canvas), but it was difficult to reproduce.

To consistently reproduce, open these three files ([error_1-and-3.graphite.txt](https://github.com/user-attachments/files/18559523/error_1-and-3.graphite.txt) and [error_2.graphite.txt](https://github.com/user-attachments/files/18559524/error_2.graphite.txt) are the two files needed) in succession on a clean Graphite instance, using `File > Open...`, in the given order:

`error_1-and-3.graphite.txt`, `error_2.graphite.txt`, and finally `error_1-and-3.graphite.txt`.

Then, in the last file (the one currently open), use the path tool to drag a point of the black ellipse (the other layers/shapes are extraneous data relative to the error).

> #2214 is a great example of the kind of situation we're looking to get bug reports for

Discord discussion: https://discord.com/channels/731730685944922173/860830913390575646/1333447293021720706

Commencez dans utility_types.rs, au niveau de la création du nœud Flatten Path mentionnée dans l’issue. Reproduisez le problème sur une instance Graphite propre en ouvrant error_1-and-3.graphite.txt, error_2.graphite.txt, puis error_1-and-3.graphite.txt, et en faisant glisser un point de l’ellipse noire avec l’outil de tracé. C’est terminé lorsque le nœud inattendu n’est pas créé et que le document s’affiche correctement.

Rédigé par le modèle d'indexation à partir du texte de l'issue.