Bug: Hammer Crashes when removing a Manifest Sub Map

[GrubPL]

Describe the bug

Seemingly whenever I try to remove a Manifest Sub Map, Hammer seems to crash

To Reproduce

1. Create a new map
2. Turn it into a "Manifest"
3. Make a new sub map in that Manifest
4. Try removing that sub map
5. See that Hammer crashes after confirming the remove dialog

Issue Map

N/A

Expected Behavior

It should properly remove the Sub Map without crashing

Operating System

Windows 11