Prevent crash from corrupt thermostat record

[rossbeazley]

The cube is unstable (i understand) and so its possible for max to stop working when this happens, boiler control will stop and things can get a little frosty ;)

output might be like

$ ~/workspace/eq3/eq3-max/bin/max 
Found cube at 192.168.10.145
Unexpected device 0cfb4d at /home/rdlb/workspace/eq3/eq3-max/bin/../lib/Max.pm line 126, <GEN2> line 7.
Can't call method "_set" on an undefined value at /home/rdlb/workspace/eq3/eq3-max/bin/../lib/Max.pm line 129, <GEN2> line 7.

even forgetting the device cant work

$ ~/workspace/eq3/eq3-max/bin/max forget 0cfb4d
Found cube at 192.168.10.145
Unexpected device 0cfb4d at /home/rdlb/workspace/eq3/eq3-max/bin/../lib/Max.pm line 126, <GEN2> line 7.
Can't call method "_set" on an undefined value at /home/rdlb/workspace/eq3/eq3-max/bin/../lib/Max.pm line 129, <GEN2> line 7

this PR simply guards against this undefined $device

and even though it looks like things are not good, the device can then be forgotten and things recover

$ ~/workspace/eq3/eq3-max/bin/max forget 0cfb4d
Found cube at 192.168.10.145
Unexpected device 0cfb4d at /home/rdlb/workspace/eq3/eq3-max/bin/../lib/Max.pm line 126, <GEN2> line 7.
Unexpected device 0ad98d at /home/rdlb/workspace/eq3/eq3-max/bin/../lib/Max.pm line 126, <GEN2> line 7.
Unexpected device 09ed2a at /home/rdlb/workspace/eq3/eq3-max/bin/../lib/Max.pm line 126, <GEN2> line 7.
Unexpected device 0bda40 at /home/rdlb/workspace/eq3/eq3-max/bin/../lib/Max.pm line 126, <GEN2> line 7.
Unexpected device 0bda32 at /home/rdlb/workspace/eq3/eq3-max/bin/../lib/Max.pm line 126, <GEN2> line 7.
Unexpected device 09ed35 at /home/rdlb/workspace/eq3/eq3-max/bin/../lib/Max.pm line 126, <GEN2> line 7.
Unexpected device 0bef2a at /home/rdlb/workspace/eq3/eq3-max/bin/../lib/Max.pm line 126, <GEN2> line 7.
Done.

$ ~/workspace/eq3/eq3-max/bin/max 
Found cube at 192.168.10.145
* Kitchen(1)         0.0 →  0.0   
* TV(2)              0.0 → 21.5    74%
* Conservatory(3)   18.2 → 19.5    65%
* Tech Room(4)       0.0 → 19.0     0%
* Hall(5)           20.0 → 20.5    25%
* Bedroom 2(6) 19.6 → 19.0    13%
* Bathroom(7)       18.6 → 19.5    20%
* Bedroom(8)         0.0 → 19.0     0%
* Office(9)     0.0 → 18.5     0%
* Loft(10)           0.0 → 18.0     0%