feat(ppsci): support data_effient_nopt

Author: xiaoyewww

examples/data_efficient_nopt/data_efficient_nopt.py

@@ -437,7 +437,7 @@ def single_dset_val(self, subset, logs, cutoff=40):
                 break
             count += 1
             input = data[0]
-            label = data[1]
+            label = data[1] if len(data) > 1 else None
 
             # unsupervised pretrain
             if self.params.mode == "train":