fix: UnboundLocalError for noise_pred_neg/perturbed when cfg=1.0

[Frank Greico (codeman101)]

Summary

Fixes UnboundLocalError in MultimodalGuider.predict_noise() when using cfg=1.0 (distilled mode) with sampler_post_cfg_function hooks active.

Fixes #458

Bug

In predict_noise(), the variables noise_pred_neg and noise_pred_perturbed are only assigned inside conditional blocks:

• noise_pred_neg is assigned inside if any(params.do_uncond() ...) -- skipped when cfg=1.0
• noise_pred_perturbed is assigned inside if any(params.do_perturbed() ...) -- skipped when STG is disabled

However, both variables are unconditionally referenced later in the sampler_post_cfg_function hooks loop:

for fn in model_options.get("sampler_post_cfg_function", []):
    args = {
        ...
        "uncond_denoised": noise_pred_neg,        # <-- UnboundLocalError
        "perturbed_cond_denoised": noise_pred_perturbed,  # <-- UnboundLocalError
    }

This causes an UnboundLocalError crash when any post-CFG hook is registered (e.g. from other custom nodes) and the model runs in distilled mode (cfg=1.0).

Fix

Initialize both variables to noise_pred_pos as safe fallbacks before the conditional blocks:

noise_pred_neg = noise_pred_pos
noise_pred_perturbed = noise_pred_pos

When cfg=1.0 and no perturbation is applied, the unconditional and perturbed predictions are semantically equivalent to the positive prediction, so noise_pred_pos is the correct fallback value.