[Fix] miss importing torchvision in torchscript wrapper (#1702)

mmdeploy/backend/torchscript/wrapper.py

@@ -1,10 +1,11 @@
 # Copyright (c) OpenMMLab. All rights reserved.
+import importlib
 import os.path as osp
 from typing import Dict, Optional, Sequence, Union
 
 import torch
 
-from mmdeploy.utils import Backend
+from mmdeploy.utils import Backend, get_root_logger
 from mmdeploy.utils.timer import TimeCounter
 from ..base import BACKEND_WRAPPER, BaseWrapper
 from .init_plugins import get_ops_path
@@ -39,10 +40,20 @@ def __init__(self,
                  model: Union[str, torch.jit.RecursiveScriptModule],
                  input_names: Optional[Sequence[str]] = None,
                  output_names: Optional[Sequence[str]] = None):
+        logger = get_root_logger()
+
         # load custom ops if exist
         custom_ops_path = get_ops_path()
         if osp.exists(custom_ops_path):
             torch.ops.load_library(custom_ops_path)
+
+        # import torchvision for ops
+        try:
+            importlib.import_module('torchvision')
+        except Exception:
+            logger.warning(
+                'Can not import torchvision. '
+                'Models require ops in torchvision might not available.')
         super().__init__(output_names)
         self.ts_model = model
         if isinstance(self.ts_model, str):