fix: return 3-tuple from predict_with_cfg use_zero_init early-exit

[laurigates]

Fixes #2010.

The CFG-Zero* early-exit in predict_with_cfg returned a 2-tuple while every caller (and every other return in the same function) unpacks 3 values: (noise_pred, noise_pred_ovi, cache_state). Workflows that enable both cfg_zero_star and use_zero_init on WanVideoExperimentalArgs crash on step 0 with:

ValueError: not enough values to unpack (expected 3, got 2)

Same shape of bug as #1454 (HUMO branch), different code path that escaped that fix.

Change

 if use_cfg_zero_star and (idx <= zero_star_steps) and use_zero_init:
-    return z*0, None
+    return z*0, None, cache_state

cache_state is passed through unchanged — at the zero-init step there is no actual cache update to record, so returning the input cache state is the natural identity. I have been running this patch locally on a Wan 2.2 14B I2V workflow with cfg_zero_star=true, use_zero_init=true and it produces correct output (step 0 noise prediction is zeroed as the CFG-Zero* design intends, subsequent steps proceed normally).

Test plan

• Reproduced the crash on main with WanVideoExperimentalArgs(cfg_zero_star=true, use_zero_init=true) wired into WanVideoSamplerv2.extra_args via WanVideoSamplerExtraArgs.
• Applied the patch and re-ran the same graph end-to-end without error.
• Verified all other returns in predict_with_cfg are 3-tuples.