Camera2D preview doesn't show correctly when parent moves

[Alex-doc]

Operating system or device - Godot version:
regarding 1566da2

Issue description (what happened, and what was expected):
The preview shows incorrect behavior if the parent node is moved

Steps to reproduce:

• add node to scene
• add another node "A" (Node2D would work)
• add a Camera2D as child in "A"
• move "A"

Link to minimal example project (optional but very welcome):
https://www.dropbox.com/s/9ivvyy9k06mrul5/cambug.zip?dl=0

[bojidar-bg]

Can confirm, would try to fix quickly...