fix

Change-Id: Id25fe7b10031ca838aa00ddc80709fdf07b8a6f1

paddle/fluid/train/custom_trainer/feed/dataset/data_reader.cc

@@ -171,7 +171,7 @@ public:
                     return -1;
                 }
             }
-            if (!_file_system) {
+            if (_file_system->err_no() != 0) {
                 _file_system->reset_err_no();
                 return -1;
             }