wan: vae: Fix light/color change (#13101)

There was an issue where the resample split was too early and dropped one
of the rolling convolutions a frame early. This is most noticable as a
lighting/color change between pixel frames 5->6 (latent 2->3), or as a
lighting change between the first and last frame in an FLF wan flow.

comfy/ldm/wan/vae.py

@@ -376,11 +376,16 @@ class Decoder3d(nn.Module):
             return
 
         layer = self.upsamples[layer_idx]
-        if isinstance(layer, Resample) and layer.mode == 'upsample3d' and x.shape[2] > 1:
-            for frame_idx in range(x.shape[2]):
+        if feat_cache is not None:
+            x = layer(x, feat_cache, feat_idx)
+        else:
+            x = layer(x)
+
+        if isinstance(layer, Resample) and layer.mode == 'upsample3d' and x.shape[2] > 2:
+            for frame_idx in range(0, x.shape[2], 2):
                 self.run_up(
-                    layer_idx,
-                    [x[:, :, frame_idx:frame_idx + 1, :, :]],
+                    layer_idx + 1,
+                    [x[:, :, frame_idx:frame_idx + 2, :, :]],
                     feat_cache,
                     feat_idx.copy(),
                     out_chunks,
@@ -388,11 +393,6 @@ class Decoder3d(nn.Module):
             del x
             return
 
-        if feat_cache is not None:
-            x = layer(x, feat_cache, feat_idx)
-        else:
-            x = layer(x)
-
         next_x_ref = [x]
         del x
         self.run_up(layer_idx + 1, next_x_ref, feat_cache, feat_idx, out_chunks)