Update modeling_qwen2.py

### **Pull Request Title**

Fix padding\_idx bug when `use_position_embedding=false` and `use_position_idx=true`

---

### **Description**

This PR fixes a bug where `self.padding_idx` is undefined if `use_position_embedding=false` and `use_position_idx=true`, since its initialization only happens inside the `if self.use_position_embedding:` block.

**Changes made:**

* Added a conditional check around lines 178–179 to avoid accessing `self.padding_idx` when position embeddings are disabled.
* Moved

```python
position_indices = position_indices.reshape(pc, self.patch_size)
```

into the `use_position_embedding` block for consistency.

These changes prevent runtime errors and keep position index reshaping aligned with the intended design.

modeling_qwen2.py

@@ -174,16 +174,17 @@ class TimeSeriesEmbedding(nn.Module):
                 padding = last_value.repeat(padding_length, 1)
                 xi = torch.cat([xi, padding], dim=0)
                 
-                # Use special padding index for padding positions
-                padding_positions = torch.full((padding_length,), self.padding_idx, device=x.device)
-                position_indices = torch.cat([position_indices, padding_positions], dim=0)
+                # Use special padding index for padding positions when use_position_embedding enabled
+                if self.use_position_embedding:
+                    padding_positions = torch.full((padding_length,), self.padding_idx, device=x.device)
+                    position_indices = torch.cat([position_indices, padding_positions], dim=0)
 
             # Reshape to patches
             xi = xi.reshape(pc, self.patch_size)  # (num_patches, patch_size)
-            position_indices = position_indices.reshape(pc, self.patch_size)  # (num_patches, patch_size)
-
+            
             if self.use_position_embedding:
                 # Collect position indices instead of calling embedding immediately
+                position_indices = position_indices.reshape(pc, self.patch_size)  # (num_patches, patch_size)
                 all_position_indices.append(position_indices)
                 patch_info_list.append({
                     'xi': xi,