LatentConcat extra frames when adding by time

### Custom Node Testing

- [ ] I have tried disabling custom nodes and the issue persists (see [how to disable custom nodes](https://docs.comfy.org/troubleshooting/custom-node-issues#step-1%3A-test-with-all-custom-nodes-disabled) if you need help)

### Expected Behavior

if I add two videos, I should get as many frames as they have

### Actual Behavior

when I use the latentconcat node for adding two WAN2.2 videos, 3 frames are inserted between them for some reason, it is unknown where they come from and they are of poor quality

### Steps to Reproduce

I just create two WAN2.2 videos in one workspace and combine them using latentconcat

### Debug Logs

```powershell
s1.shape=torch.Size([1, 16, 21, 49, 90]), s2.shape=torch.Size([1, 16, 21, 49, 90]), dim=t
```

### Other

_No response_