AMRNAV-3826 Fix for nav2_velocity_smoother

[HovorunB]

---

Basic Info

Info	Fix for nav2_velocity_smoother
Ticket(s) this addresses	(add tickets here #1)
Primary OS tested on	(Ubuntu, MacOS, Windows)
Robotic platform tested on	(Steve's Robot, gazebo simulation of Tally, hardware turtlebot)

---

Related deep_cv PR: https://github.com/logivations/deep_cv/pull/4793

Description of contribution in a few bullet points

• Added condition to fix an error when using sim time

---

For Maintainers:

• Check that any new parameters added are updated in navigation.ros.org
• Check that any significant change is added to the migration guide
• Check that any new features OR changes to existing behaviors are reflected in the tuning guide
• Check that any new functions have Doxygen added
• Check that any new features have test coverage
• Check that any new plugins is added to the plugins page
• If BT Node, Additionally: add to BT's XML index of nodes for groot, BT package's readme table, and BT library lists

[tonynajjar]

Can you please clarify to me how the condition being none contributes to command_ being null? command_ is not in the condition

[HovorunB]

Can you please clarify to me how the condition being none contributes to command_ being null? command_ is not in the condition

If we use sim time the condition is false on startup. And if the condition is false we proceed to access command_'s properties which leads to an error since command_ is a nullptr on startup

[tonynajjar]

Please fix like it was fixed in upstream