[2.0.0 Beta 2] Different size background doesn't update editable area until restart

[JamesParkNINJA]

Describe the bug
When you switch to a background that's a different size from the default a new scene picks, the new size doesn't get auto-calc'd properly and triggers snap to the bottom of the old size (until you close and reopen).

To Reproduce
Steps to reproduce the behavior:

1. Create a new Scene (by default it would take a 160x144 background)
2. Switch background to larger size (160x288 in my case)
3. Add an actor/trigger to the scene
4. Try to move it to the bottom of the scene
5. Editable parts of scene still locked to old background size

Expected behavior
The editor should update the editable area based on background size selected

Screenshots

Platform (please complete the following information):

• OS: Windows 10
• App version 2.0.0 Beta 2

[RichardULZ]

Oh no is this related to the older scene hasn't updated dimensions from replaced image bug? #386

Hmm, seems not, I have replicated your new bug by Switching a scenes background from the dropdown options for the scene within the editor, not externally like in #386 (which seems to be fixed? will investigate)

The scene must be small when placed in the background, and be changed to a larger background to reproduce the bug. Copying and pasting the scene does not fix the issue, Reload assets does not fix this issue, saving and using File Open does solve the issue for placed scenes.

[chrismaltby]

This is pretty embarrassing bug introduced when I rewrote a lot of the backend recently, I actually did write a load of tests around this area but missed writing a test for this specific bit of functionality :-(

I've just merged a two line fix in #566 could you confirm this works for you now with the latest dev build?

[chrismaltby]

This fix is now deployed in beta3 :-)