Ignore released shaders when inhibiting frame elision

[hkf57]

What changed

Ignore released shader slots when checking whether an incomplete texture must inhibit frame elision.

if (auto* sh = shaderList[idx]; sh && sh->refCount > 0)

Why

When an asynchronous texture is released before upload completes, r_shaderHnd_c aborts the load at reference count zero. Depending on its loading phase, the cancelled texture can remain INIT or PENDING_UPLOAD; PurgeShaders() deliberately retains shader slots until their texture is DONE.

PumpShaders() scans those released slots and currently sets inhibitElision for any non-DONE texture. Since the cancelled texture will never finish, EndFrame() clears lastFrameHash every frame and permanently defeats identical-frame elision.

Released shaders cannot participate in rendering. Restricting the loading check to positive-reference slots preserves elision inhibition for every active loading texture while excluding abandoned slots.

Closes #108.

Live evidence

On the reproducing PoB build, SimpleGraphic's Layers panel reported:

• 122 out of 122 frames drawn
• Elide identical frames enabled
• Elision inhibited continuously true

The affected focused 3840x1600 window used roughly 80% of an RTX 3080 Ti. The same instance at 1296x759 used 1.26%, and another maximized build using the same executable/runtime used 2.57%. DWM, refresh rate, NVIDIA profile matching, and overlays were excluded as the primary discriminator.

Validation

• git diff --check: passed
• Fork Windows 2022 build workflow: passed (run 30789884304)
• Runtime version: 2.5-dad6573
• Portable test foreground PID verified before and after the performance sample
• Patched focused/maximized GPU 3D: 6.27% average / 8.82% maximum, down from 80.7% average with stock/first candidate (about 92% lower)
• Renderer Layers panel after fix: 22 out of 1020 frames drawn, frame elision enabled, Elision inhibited false

The portable process was closed after the sample and the original focus/cursor were restored. No installed PoB files or persistent settings were changed.