Fix trust ratio in lamb (#17614)

test=develop

paddle/fluid/operators/optimizers/lamb_op.h

@@ -174,10 +174,11 @@ struct LambParamUpateFunctor {
 
   inline HOSTDEVICE void operator()(size_t i) const {
     T lr = *lr_;
-    T p_norm = *param_norm_;
-    T tr_div_norm = *trust_ratio_div_norm_;
+    T p = *param_norm_;
+    T t = *trust_ratio_div_norm_;
 
-    lr *= p_norm / tr_div_norm;
+    T r = (p > 0 && t > 0) ? p / t : 1.0;
+    lr *= r;
     param_out_[i] = param_[i] - lr * trust_ratio_div_[i];
   }
 };