Prevent thread to being created every time a goal is published

crosbot_explore/src/nodes/astar_explorer_node.cpp

@@ -223,7 +223,9 @@ void AStarExplorerROSNode::handleExploreMode(crosbot_explore::SetExplorerModeReq
 
             // Start planning thread
             planningOperating = true;
+            if( !planningThread->isAlive() ){
                 planningThread->start();
+            }
         } else {
             ROS_ERROR("%s No pose provided for A* goal", LOG_START);
             response.success = false;