Crash when duplicating ShaderMaterial or when making it local to scene

[Armynator]

Tested versions

#90161 broke duplicating ShaderMaterials

Reproducible on 9286ac7
Not reproducible on c205f02

System information

Godot v4.3.dev (9286ac7) - Windows 10.0.22631 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3080 Ti (NVIDIA; 31.0.15.5176) - Intel(R) Core(TM) i9-14900K (32 Threads)

Issue description

When trying to duplicate a ShaderMaterial resource by script (either GDScript or C#), the game crashes at runtime.
editor_log.txt

An alternative way to crash it is to just mark "Local to Scene" in the Resource dropdown of the ShaderMaterial in the editor.
editor_log_2.txt

Steps to reproduce

1. Create a ShaderMaterial and assign it to a MeshInstance3D
2. Add a script to the MeshInstance3D
3. Call material_override.duplicate() in _ready() in the script attached to the MeshInstance3D
4. Run the game and notice the crash

Another way to crash:

1. Create a ShaderMaterial and assign it to a MeshInstance3D
2. Don't add a script but mark "Local to Scene" in the ShaderMaterial Resource dropdown in editor
3. Run the game and notice the crash

Minimal reproduction project (MRP)

Minimal project with just a ShaderMaterial and a script that calls duplicate on it.
shader_mat_repro.zip

You can use the same project to reproduce both crashes. Simply remove the script from the MeshInstance3D and mark Local to Scene for the ShaderMaterial before running the game.