[smoother] potentially invalid first "last command" when not using velocity feedback

[bit-pirate]

When no velocity feedback is used, it looks like the last_cmd_vel is not valid until the smoother did one spin. That is, last_cmd_vel is after start up 0 and afterwards what ever the last command was.

This could result into a strange first smoothing result.

[bit-pirate]

FYI @corot

@AlexReimann not important for us right now, since we usually use odometry feedback.

[AlexReimann]

We don't use odometry feedback usually because the long execution delay..