Blender Git Loki

Fix: Potential use after scope in curve to mesh node

I don't think this has been visible, since I only ran into it after
changing other code that affected this. However, some attributes
can keep a reference to the source component to use when tagging
caches dirty (like the position attribute tagging the normals dirty).
Here, the component was created inside a function, then the attributes
were used afterwards.

Also add some comments warning about this in the header file.