fix img_shape (#719)

Author: liuyanyi

mmrotate/datasets/transforms/transforms.py

@@ -151,7 +151,8 @@ def _transform_bboxes(self, results: dict) -> None:
 
     def _filter_invalid(self, results: dict) -> None:
         """Filter invalid data w.r.t `gt_bboxes`"""
-        height, width = results['img_shape']
+        # results['img_shape'] maybe (h,w,c) or (h,w)
+        height, width = results['img_shape'][:2]
         if 'gt_bboxes' in results:
             if len(results['gt_bboxes']) == 0:
                 return