Camera Pan Restricted Coordinates after Background File Change

[SetsuneW]

Describe the bug
Camera cannot pan past smaller X,Y limits when scene background file is directly replaced with a larger one.

To Reproduce

1. Create a scene with a smaller map.
2. Copy-and-Paste a same-named file overwriting the existing background image file with a larger one.
3. The preview will expand automatically in the Editor, and most things seem to work normally.
4. However, trying to pan the camera using code commands to move it beyond the original bounds won't work. (I only tested X). It seems to stay restricted to the original X,Y dimensions of the initial image.

Saving, closing, and reloading doesn't seem to fix the problem. Swapping to a new background and then back perhaps fixed it, but that could be destructive to existing map elements.

My guess is the editor doesn't update the camera bounds stored somewhere when it realizes the dimensions of the background image have changed.

Expected behavior
Camera can pan to coordinates beyond the original background image's size if the updated background is larger.

Screenshots
Here is an attached example of the issue in action. I created the scene using the "Small" file, then copied over the "Big" one.
CameraPan2.zip

Platform (please complete the following information):

• OS: Windows 10 Home Version 1909 (OS Build 18363.815)
• App version 1.2.1, Develop Branch, Commit 226c4d

Additional context
This may be related to #386, but is not fixed by saving and reloading.