USERDATA does not work when using GPU trails

[ueshita]

Tested versions

4.3.beta2

System information

Godot v4.3.beta2 - Windows 10.0.22631 - Vulkan (Forward+) - integrated AMD Radeon(TM) Graphics (Advanced Micro Devices, Inc.; 31.0.12027.9001) - AMD Ryzen 9 6900HX with Radeon Graphics (16 Threads)

Issue description

I found that USERDATA does not behave correctly when using GPUParticles3D's trail mode.
I have written to USERDATA1 in start() and read it in process() but cannot get the correct value.
It seemed to affect the initial value of the particle buffer.

Here is the Particle shader code.

shader_type particles;

void start() {
	TRANSFORM = EMISSION_TRANSFORM;
	CUSTOM = vec4(0.0);
	VELOCITY = vec3(0.0, 10.0, 1.0);

	USERDATA1.x = 0.5;
}

void process() {
	TRANSFORM[0][0] = 1.0 - USERDATA1.x;  // this will be invalid data when the trail.

	CUSTOM.x += DELTA;
	if (CUSTOM.x > LIFETIME) {
		ACTIVE = false;
	}
}

Left: Trails is not correctly (X scale is 1.0 or invalid value)
Right: Particles is correctly (X scale is 0.5)

Steps to reproduce

• Set GPUParticles3D in trail mode
• Set up particle shader
• Write USERDATA1 in start()
• Read USERDATA1 in process()

Minimal reproduction project (MRP)

bug_trails_using_userdata.zip