### 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
atlas_rect_norm.size /= directional_shadow_size;
		light_storage->light_instance_set_directional_shadow_atlas_rect(p_light, p_pass, atlas_rect_norm);
		zfar = RSG::light_storage->light_get_param(base, RS::LIGHT_PARAM_RANGE);
		render_fb = light_storage->direction_shadow_get_fb();
		render_texture = RID();
		flip_y = true;
	} else {
		
		ERR_FAIL_COND(!light_storage->owns_shadow_atlas(p_shadow_atlas));
		ERR_FAIL_COND(!light_storage->shadow_atlas_owns_light_instance(p_shadow_atlas, p_light));
		RSG::light_storage->shadow_atlas_update(p_shadow_atlas);
		uint32_t key = light_storage->shadow_atlas_get_light_instance_key(p_shadow_atlas, p_light);
		uint32_t quadrant = (key >> RendererRD::LightStorage::QUADRANT_SHIFT) & 0x3;
		uint32_t shadow = key & RendererRD::LightStorage::SHADOW_INDEX_MASK;
		uint32_t subdivision = light_storage->shadow_atlas_get_quadrant_subdivision(p_shadow_atlas, quadrant);
		ERR_FAIL_INDEX((int)shadow, light_storage->shadow_atlas_get_quadrant_shadow_size(p_shadow_atlas, quadrant));
		uint32_t shadow_atlas_size = light_storage->shadow_atlas_get_size(p_shadow_atlas);
		uint32_t quadrant_size = shadow_atlas_size >> 1;
		atlas_rect.position.x = (quadrant & 1) * quadrant_size;
		atlas_rect.position.y = (quadrant >> 1) * quadrant_size;
		uint32_t shadow_size = (quadrant_size / subdivision);
		atlas_rect.position.x += (shadow % subdivision) * shadow_size;
		atlas_rect.position.y += (shadow / subdivision) * shadow_size;
		atlas_rect.size.width = shadow_size;
		atlas_rect.size.height = shadow_size;
		zfar = light_storage->light_get_param(base, RS::LIGHT_PARAM_RANGE);
		if (light_storage->light_get_type(base) == RS::LIGHT_OMNI) {
			bool wrap = (shadow + 1) % subdivision == 0;
			dual_paraboloid_offset = wrap ? Vector2i(1 - subdivision, 1) : Vector2i(1, 0);
			if (light_storage->light_omni_get_shadow_mode(base) == RS::LIGHT_OMNI_SHADOW_CUBE) {