### Godot version

4.0.2 stable

### System information

issue tested on win10 with ryzen 7 and rx 6600, win11 with ryzen 7 and gtx 3050

### Issue description

When creating a screen reading post processing shader, the normal buffer functions correctly in the editor, but does not seem to be functioning as expected in debug, producing only a solid colour when run. I am unsure if this behaviour is intended, but if so, I feel it should be properly documented.

Running correctly in editor:
![image](https://user-images.githubusercontent.com/71034402/230672620-fc5e4baf-c12e-4755-b7a2-206087459307.png)

Solid colour in debug:
![image](https://user-images.githubusercontent.com/71034402/230672489-d9c29755-c2d3-4e72-9ea0-355148e916fe.png)


### Steps to reproduce

*this shader should be attached to a MeshInstance3D quadmesh*
minimal shader to reproduce:

```glsl
shader_type spatial;
render_mode unshaded, cull_disabled;

uniform sampler2D NORMAL_TEXTURE : hint_normal_roughness_texture, filter_linear_mipmap;

void vertex(){
	VERTEX *= 2.0;
	POSITION = vec4(VERTEX, 1.0);
}

void fragment(){
	ALBEDO = texture(NORMAL_TEXTURE, SCREEN_UV).rgb;
}
```

### Minimal reproduction project

N/A
render_texture = light_storage->get_cubemap(shadow_size / 2);
				render_fb = light_storage->get_cubemap_fb(shadow_size / 2, p_pass);
				light_projection = light_storage->light_instance_get_shadow_camera(p_light, p_pass);
				light_transform = light_storage->light_instance_get_shadow_transform(p_light, p_pass);
				render_cubemap = true;
				finalize_cubemap = p_pass == 5;
				atlas_fb = light_storage->shadow_atlas_get_fb(p_shadow_atlas);
				atlas_size = shadow_atlas_size;
				if (p_pass == 0) {
					_render_shadow_begin();
				}
			} else {
				atlas_rect.position.x += 1;
				atlas_rect.position.y += 1;
				atlas_rect.size.x -= 2;
				atlas_rect.size.y -= 2;
				atlas_rect.position += p_pass * atlas_rect.size * dual_paraboloid_offset;
				light_projection = light_storage->light_instance_get_shadow_camera(p_light, 0);
				light_transform = light_storage->light_instance_get_shadow_transform(p_light, 0);
				using_dual_paraboloid = true;
				using_dual_paraboloid_flip = p_pass == 1;
				render_fb = light_storage->shadow_atlas_get_fb(p_shadow_atlas);
				flip_y = true;
			}
		} else if (light_storage->light_get_type(base) == RS::LIGHT_SPOT) {
			light_projection = light_storage->light_instance_get_shadow_camera(p_light, 0);
			light_transform = light_storage->light_instance_get_shadow_transform(p_light, 0);
			render_fb = light_storage->shadow_atlas_get_fb(p_shadow_atlas);
			flip_y = true;
		}