Extend the lifetime of waitables by holding onto the shared pointer.

Otherwise, you can get into a situation where the waitable
has actually been freed before you try to access it later.

Signed-off-by: Chris Lalancette <clalancette@openrobotics.org>

rclcpp/include/rclcpp/strategies/allocator_memory_strategy.hpp

@@ -187,7 +187,7 @@ class AllocatorMemoryStrategy : public memory_strategy::MemoryStrategy
         group->find_waitable_ptrs_if(
           [this](const rclcpp::Waitable::SharedPtr & waitable) {
             waitable_handles_.push_back(waitable);
-            return false;
+            return true;
           });
       }
     }