Guard against calling null goal response callback (#738)

Also make sure to invoke the goal response callback before the result callback.

Signed-off-by: Jacob Perron <jacob@openrobotics.org>
Signed-off-by: Siddharth Kucheria <kucheria@usc.edu>

rclcpp_action/include/rclcpp_action/client.hpp

@@ -368,21 +368,23 @@ class Client : public ClientBase
         // Do not use std::make_shared as friendship cannot be forwarded.
         std::shared_ptr<GoalHandle> goal_handle(
           new GoalHandle(goal_info, options.feedback_callback, options.result_callback));
+        {
+          std::lock_guard<std::mutex> guard(goal_handles_mutex_);
+          goal_handles_[goal_handle->get_goal_id()] = goal_handle;
+        }
+        promise->set_value(goal_handle);
+        if (options.goal_response_callback) {
+          options.goal_response_callback(future);
+        }
+
         if (options.result_callback) {
           try {
             this->make_result_aware(goal_handle);
           } catch (...) {
             promise->set_exception(std::current_exception());
-            options.goal_response_callback(future);
             return;
           }
         }
-        std::lock_guard<std::mutex> guard(goal_handles_mutex_);
-        goal_handles_[goal_handle->get_goal_id()] = goal_handle;
-        promise->set_value(goal_handle);
-        if (options.goal_response_callback) {
-          options.goal_response_callback(future);
-        }
       });
     return future;
   }