Set frame_id and stamp on Path message even if path is not found.

[ledmonster]

When path planning is failed, global planner publishes nav_msgs::Path without frame_id and stamp now. It causes error on rviz. Fix it to publish nav_msgs::Path with frame_id and stamp even if path planning was failed.

Before:

header: 
  seq: 24
  stamp: 
    secs: 0
    nsecs:         0
  frame_id: ''
poses: []

After:

header: 
  seq: 122
  stamp: 
    secs: 1477468563
    nsecs: 495041114
  frame_id: map
poses: []

[mikeferguson]

I can't see any downside to this, but @DLu is there a reason that this initially had that if() block?

[DLu]

If there was, I don't remember it anymore.
+1

[ledmonster]

Thank you!