fix model export when early stop=weight diff(#4659)

Signed-off-by: Yu Wu <yolandawu131@gmail.com>
Signed-off-by: sagewe <wbwmat@gmail.com>

python/fate/ml/utils/_convergence.py

@@ -78,7 +78,10 @@ def __init__(self, eps):
     def is_converge(self, delta_weight, weight=None):
         weight_diff = torch.linalg.norm(delta_weight, 2)
         if weight is None:
-            return weight_diff < self.eps
+            # avoid tensor[bool]
+            if weight_diff < self.eps:
+                return True
+            return False
         if self.pre_weight is None:
             self.pre_weight = weight
             return False