[Bugfix] Fix Idefics3 fails during multi-image inference (#11080)

Signed-off-by: B-201 <Joy25810@foxmail.com>

vllm/model_executor/models/idefics3.py

@@ -60,7 +60,8 @@ class Idefics3ImagePixelInputs(TypedDict):
     type: Literal["pixel_values"]
     data: torch.Tensor
     """
-    Shape: `(batch_size * num_images, num_channels, height, width)`
+    Shape: `(batch_size * num_images * num_patches, 
+             num_channels, height, width)`
     """
     pixel_attention_mask: Optional[torch.BoolTensor]
 
@@ -520,13 +521,17 @@ class Idefics3Model(nn.Module):
                 raise ValueError("Incorrect type of pixel values. "
                                  f"Got type: {type(pixel_values)}")
 
-            return Idefics3ImagePixelInputs(type="pixel_values",
-                                            data=self._validate_pixel_values(
-                                                flatten_bn(pixel_values,
-                                                           concat=True)),
-                                            pixel_attention_mask=flatten_bn(
-                                                pixel_attention_mask,
-                                                concat=True))
+            if isinstance(pixel_values, list):
+                pixel_values = torch.cat(pixel_values, dim=1)
+                pixel_attention_mask = torch.cat(pixel_attention_mask, dim=1)
+            else:
+                pixel_values = flatten_bn(pixel_values)
+                pixel_attention_mask = flatten_bn(pixel_attention_mask)
+
+            return Idefics3ImagePixelInputs(
+                type="pixel_values",
+                data=self._validate_pixel_values(pixel_values),
+                pixel_attention_mask=pixel_attention_mask)
 
         raise AssertionError("This line should be unreachable.")