Drawing by appending to the selected layer fails on empty layers

You can use the Pen, Spline, or Freehand tool to draw while holding Shift to append to an existing selected layer of vector content. But if you create a brand new layer and draw on it with Shift held, this is the result:


Whereas this is the normal result of drawing (where a new layer appears):


So we need to detect if no existing vector data is there, and if so, add the Path and Stroke nodes instead of the Flatten Vector Elements node.

It also needs to work on "empty" layers that do contain modifier nodes, like this:


Currently, append-drawing results in this:


But the desired output in this case should be:


Reproduce el problema con la herramienta Pen, Spline o Freehand mientras mantienes pulsada la tecla Shift en una capa nueva y vacía; después, repite la prueba con una capa vacía que contenga nodos modifier. Rastrea el procesamiento de append-drawing y verifica que las capas vacías creen nodos Path y Stroke en lugar de Flatten Vector Elements, conservando los nodos modifier.

Escrito por el modelo de indexación a partir del texto del issue.