Reset timer trigger time before execute.

This PR fixes an issue with StaticSingleThreadedExecutor
not reseting the timers, so they were always ready
and executing callbacks continuosly.

ros2#1692

Signed-off-by: Mauro Passerino <mpasserino@irobot.com>

rclcpp/src/rclcpp/executors/static_single_threaded_executor.cpp

@@ -237,7 +237,9 @@ StaticSingleThreadedExecutor::execute_ready_executables(bool spin_once)
   for (size_t i = 0; i < wait_set_.size_of_timers; ++i) {
     if (i < entities_collector_->get_number_of_timers()) {
       if (wait_set_.timers[i] && entities_collector_->get_timer(i)->is_ready()) {
-        execute_timer(entities_collector_->get_timer(i));
+        auto timer = entities_collector_->get_timer(i);
+        timer->call();
+        execute_timer(std::move(timer));
         if (spin_once) {
           return true;
         }