fix ClearTensorArray; (#7286)

Author: zhangjun

lite/api/light_api.cc

@@ -401,8 +401,9 @@ void LightPredictor::ClearTensorArray(
       const cpp::VarDesc* var = block->GetVar<cpp::VarDesc>(var_idx);
       CHECK(var);
 
-      auto tmp = program_->exec_scope()->FindVar(var->Name());
-      if (tmp->IsType<std::vector<Tensor>>()) {
+      auto* var_ptr = program_->exec_scope()->FindVar(var->Name());
+      if (var_ptr->IsType<std::vector<Tensor>>() &&
+          (var->Name() != "feed" && var->Name() != "fetch")) {
         std::vector<Tensor>* tensor_array_var =
             program_->exec_scope()->FindMutableTensorList(var->Name());
         CHECK(tensor_array_var);