fix_eval, test=dygraph (#2082)

dygraph/ppdet/engine/trainer.py

@@ -97,8 +97,8 @@ class Trainer(object):
     def _init_metrics(self):
         if self.mode == 'eval':
             if self.cfg.metric == 'COCO':
-                mask_resolution = self.model.mask_post_process.mask_resolution if hasattr(
-                    self.model, 'mask_post_process') else None
+                mask_resolution = self.model.mask_post_process.mask_resolution if getattr(
+                    self.model, 'mask_post_process', None) else None
                 self._metrics = [
                     COCOMetric(
                         anno_file=self.dataset.get_anno(),