### Godot version

v4.0 rc6

### System information

Windows 10

### Issue description

When using a ViewportTexture from a SubViewport on a TextureRect, it throws errors after running the scene once and then switching scenes in the editor.
![Pasted image 20230227212626](https://user-images.githubusercontent.com/44676282/221680047-984fa03e-33d1-4856-9a7f-1700b28423cf.png)


### Steps to reproduce

Run the canvas-scene once.
Switch to another scene in the editor.
Switch back to the canvas-scene

### Minimal reproduction project

[ViewportTextureError.zip](https://github.com/godotengine/godot/files/10844099/ViewportTextureError.zip)

ERR_MAIN_THREAD_GUARD;
	if (camera_3d_override) {
		if (camera_3d_override.fov == p_fovy_degrees && camera_3d_override.z_near == p_z_near &&
				camera_3d_override.z_far == p_z_far && camera_3d_override.projection == Camera3DOverrideData::PROJECTION_PERSPECTIVE) {
			return;
		}
		camera_3d_override.fov = p_fovy_degrees;
		camera_3d_override.z_near = p_z_near;
		camera_3d_override.z_far = p_z_far;
		camera_3d_override.projection = Camera3DOverrideData::PROJECTION_PERSPECTIVE;
		RenderingServer::get_singleton()->camera_set_perspective(camera_3d_override.rid, camera_3d_override.fov, camera_3d_override.z_near, camera_3d_override.z_far);
	}
}
void Viewport::set_camera_3d_override_orthogonal(real_t p_size, real_t p_z_near, real_t p_z_far) {