return complete object on scan read (AngleInDegrees) timeout

[brannonvann]

It was returning incorrect structure upon timeout or no data available when reading scan (AngleInDegrees). This caused an error in the neato_node.

Traceback (most recent call last):
  File "/home/ubuntu/catkin_ws/src/intro_to_ros/bv80bot/neato_robot/neato_node/nodes/neato.py", line 209, in <module>
    robot.spin()
  File "/home/ubuntu/catkin_ws/src/intro_to_ros/bv80bot/neato_robot/neato_node/nodes/neato.py", line 119, in spin
    scan.ranges, scan.intensities = self.robot.getScanRanges()
ValueError: need more than 0 values to unpack

I experienced this on 2 different model Neatos. If I slowed the reading of the data I never experienced this problem and previously on a slower raspberry pi I did not notice this issue. I assume I'm seeing it now because the raspberry pi is processing faster than the neato can respond but I'm really not sure. The fix included in my commit resolves the issue.