### Godot version

v4.0.beta.custom_build [291add339]

### System information

Windows 10, Forward+, NVIDIA GeForce GTX 1050 Ti (31.0.15.1694)

### Issue description

I was testing if #69669 was solved by #70418, which it seemed to be. However, I got a wall of errors at the same time.

In the minimal reproduction project below in this Issue, I get errors when instantiating many of the same `GPUParticle2D` scene. In my earlier Godot 4 build (v4.0.beta.custom_build [2a04b18d3]) I did not get any errors (but got the occasional artifact as was my original issue in #69669).

I suspect the PR #70418 solved the artifact, but possibly introduced new bugs. However, I have not specifically built Godot with, and without the PR in question.

I believe this is the start and end of the errors - after which they repeat.
![wall_of_errors](https://user-images.githubusercontent.com/10490534/209046500-9813150c-d6e4-4a11-8e62-79d370d07009.png)

### Steps to reproduce

- Create a GPUParticle2D scene
- Instantiate the scene several times
- Observe the debugger get flooded with errors

### Minimal reproduction project

This project only instantiates default GPUParticle2D scenes with a default particle material.
[GPU_Particle_Creation_Bug.zip](https://github.com/godotengine/godot/files/10283416/GPU_Particle_Creation_Bug.zip)

if (ci->copy_back_buffer && canvas_group_owner == nullptr) {
			backbuffer_copy = true;
			if (ci->copy_back_buffer->full) {
				back_buffer_rect = Rect2();
			} else {
				back_buffer_rect = ci->copy_back_buffer->rect;
			}
		}
		RID material = ci->material_owner == nullptr ? ci->material : ci->material_owner->material;
		if (material.is_valid()) {
			CanvasMaterialData *md = static_cast<CanvasMaterialData *>(material_storage->material_get_data(material, RendererRD::MaterialStorage::SHADER_TYPE_2D));
			if (md && md->shader_data->valid) {
				if (md->shader_data->uses_screen_texture && canvas_group_owner == nullptr) {
					if (!material_screen_texture_cached) {
						backbuffer_copy = true;
						back_buffer_rect = Rect2();
						backbuffer_gen_mipmaps = md->shader_data->uses_screen_texture_mipmaps;
					} else if (!material_screen_texture_mipmaps_cached) {
						backbuffer_gen_mipmaps = md->shader_data->uses_screen_texture_mipmaps;
					}
				}
				if (md->shader_data->uses_sdf) {
					r_sdf_used = true;
				}
				if (md->shader_data->uses_time) {
					time_used = true;
				}
			}
		}
		if (ci->skeleton.is_valid()) {