Improve the check by counting num async children

Author: AndyZe

src/xml_parsing.cpp

@@ -543,15 +543,23 @@ void VerifyXML(const std::string& xml_text,
         }
         if(name == "ReactiveSequence")
         {
-          const std::string child_name = node->FirstChildElement()->Name();
-          const auto child_search = registered_nodes.find(child_name);
-          auto child_type = child_search->second;
-          if(child_type == NodeType::CONTROL &&
-             ((child_name == "ThreadedAction") || (child_name == "StatefulActionNode") ||
-              (child_name == "CoroActionNode") || (child_name == "AsyncSequence")))
+          size_t async_count = 0;
+          for(auto child = node->FirstChildElement(); child != nullptr;
+          child = child->NextSiblingElement())
           {
-            ThrowError(line_number, std::string("The first child of a ReactiveSequence "
-                                                "cannot be asynchronous"));
+            const std::string child_name = node->FirstChildElement()->Name();
+            const auto child_search = registered_nodes.find(child_name);
+            auto child_type = child_search->second;
+            if(child_type == NodeType::CONTROL &&
+              ((child_name == "ThreadedAction") || (child_name == "StatefulActionNode") ||
+                (child_name == "CoroActionNode") || (child_name == "AsyncSequence")))
+            {
+              ++async_count;
+              if (async_count > 1)
+              {
+                ThrowError(line_number, std::string("A ReactiveSequence cannot have more than one async child."));
+              }
+            }
           }
         }
       }