restore weight by default for qat quantizer (#3992)

nni/algorithms/compression/pytorch/quantization/quantizers.py

@@ -563,14 +563,13 @@ class QAT_Quantizer(Quantizer):
                 calibration_config[name]['tracked_max_input'] = float(module.tracked_max_input)
 
                 # Recover weight/bias for batch normalization folding
-                if hasattr(module, BN_FOLD_TAG):
                 actual_weight = getattr(module, 'old_weight', None)
                 if actual_weight is None:
                     logger.warning("Can not recover weight for layer %s. "
                                    "This may lead to a wrong accuracy performance on the backend.", name)
                 delattr(module, 'weight')
                 module.register_parameter('weight', actual_weight)
-
+                if hasattr(module, BN_FOLD_TAG):
                     actual_bias = getattr(module, 'old_bias', None)
                     delattr(module, 'bias')
                     if actual_bias is not None: