refine GetOrCreateVariable

paddle/framework/scope.cc

@@ -34,15 +34,17 @@ Variable* Scope::GetVariable(const std::string &name) const {
 }
 
 Variable* Scope::GetOrCreateVariable(const std::string &name) {
-  Variable* var;
-  var = GetVariable(name);
-  if (var == nullptr) {
-    auto err = CreateVariable(name);
+  Variable* var = GetVariable(name);
+  if (var != nullptr) {
+    return var;
+  }
+
+  Error err = CreateVariable(name);
   if (!err.isOK()) {
     return nullptr;
-    }
-  }
+  } else {
     return GetVariable(name);
+  }
 }
 
 bool Scope::HaveVariable(const std::string &name) {