Imgui: Not possible to undock

[sonoro1234]

In last docking branch:
https://github.com/ocornut/imgui/commit/3b3af6b73136a03dfcdb84872fc08542900a1aa8
It is not possible to undock docked windows.

It worked correctly in
https://github.com/ocornut/imgui/commit/7ddc1adefbdca94e7de350653def7a647ff45612

(I have not bisected so could work in between)

[ocornut]

Confirmed bug introduced by last merge, working on it.

[ocornut]

Should be fixed now, let us know if you stumble on anything else as the code is not trivial (7b3d379819c487f0d5323ed7bd7c9109a2bc1d76 was pretty risky but moving us in a better, more explicit direction).

[sonoro1234]

Yes, it is fixed