fix: initialize multimodal guider post-hook fallbacks at cfg=1

[Nianze Wu (wunianze666-netizen)]

Summary

This PR fixes an uninitialized fallback in MultimodalGuider.predict_noise() when cfg=1 or stg=0 and a sampler post-CFG hook is present.

Problem

oise_pred_neg and
oise_pred_perturbed are only assigned inside the unconditional / perturbed branches, but they are later passed to sampler_post_cfg_function hooks unconditionally. In distilled workflows this can surface as an UnboundLocalError when the negative branch is skipped.

Changes

• initialize packed
  oise_pred_neg and
  oise_pred_perturbed to
  oise_pred_pos before the optional branches
• preserve the existing behavior for cases where negative / perturbed predictions are actually computed

Verification

• python -m py_compile guiders/multimodal_guider.py guiders/parameters.py tricks/nodes/ltx_pag_node.py
• Not run: there does not appear to be a lightweight local test target for this guider path in the current environment.