fixed input size handling of the parts

cvfinetune/finetuner/mixins/dataset.py

@@ -38,13 +38,11 @@ class _DatasetMixin(BaseMixin):
         self.dataset_cls = dataset_cls
         self.dataset_kwargs_factory = dataset_kwargs_factory
 
-        self.input_size = Size(input_size)
-
         if part_input_size is None:
-            self.part_input_size = self.input_size
+            part_input_size = input_size
 
-        else:
-            self.part_input_size = Size(self.part_input_size)
+        self.input_size = Size(input_size)
+        self.part_input_size = Size(part_input_size)
 
         self._label_shift = label_shift