Blender Git Loki

Fix T93555: crash when muting nodes with multiple internal links

The crash happened because I was incorrectly and inconsistently assuming
that a socket is part of at most one internal link. However, this is not the case.
In geometry nodes, an input socket can be internally linked to multiple
output sockets. In the general case, an output could also be linked to multiple
input sockets, even though we don't have that in Blender yet.