[fx]Early return if a node tries prepend self (#67068)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/67068
Prepending a node to itself will result in the node gets removed from the graph.
Usually people won't prepend a node with itself. But people would accidentally try to append a node that's already next to `self` node, which will be prepending `self` to `self`.
Test Plan: Added a unit test
Reviewed By: jamesr66a
Differential Revision: D31849030
fbshipit-source-id: b0fdfbb893f785f268595acd823b426d57c15e61
