Update pdf_extract_kit.py

Modify line 397 to ensure compatibility with CPU execution, addressing the issue where specifying 'cpu' in config.json still results in a ValueError for expecting a cuda device but getting 'cpu' during demo execution.

magic_pdf/model/pdf_extract_kit.py

@@ -393,7 +393,7 @@ class CustomPEKModel:
             elif int(res['category_id']) in [5]:
                 table_res_list.append(res)
 
-        if torch.cuda.is_available():
+        if torch.cuda.is_available() and self.device != 'cpu':
             properties = torch.cuda.get_device_properties(self.device)
             total_memory = properties.total_memory / (1024 ** 3)  # 将字节转换为 GB
             if total_memory <= 10: