Prevent to make UndoRedo for duplicate if no selected node
Prevent to make UndoRedo for duplicate if no selected node

(cherry picked from commit d82928eb494d3d0856eac85e82b9cd835a368f96)

pixelpicosean/my-godot-2.1,pixelpicosean/my-godot-2.1,pixelpicosean/my-godot-2.1,pixelpicosean/my-godot-2.1,pixelpicosean/my-godot-2.1