cu2d-check-stalled-mps fails if lp target branch not found

The cu2d-check-stalled-mps script throws an exception and fails to process additional MPs if it encounters a project that doesn't map to a launchap branch (see log).

Fix should be to gracefully handle this error so that the entire stack is processed and find a way to report on these missing branches as it means the config is out of sync.

[log]
+ ./cu2d-check-stalled-mps -t 75 -d ../stacks/head/webapp.cfg
2013-07-15 15:05:55,268 DEBUG Debug mode enabled
2013-07-15 15:05:56,451 DEBUG Loading default stack configuration from ./config/defaults.conf
2013-07-15 15:05:56,460 DEBUG Loading stack configuration from ../stacks/head/webapp.cfg
2013-07-15 15:05:56,503 INFO Looking at lp:unity-webapps-googledocs
2013-07-15 15:05:56,988 INFO Looking at lp:unity-webapps-qml
2013-07-15 15:05:57,667 INFO Looking at lp:unity-webapps-youtube
2013-07-15 15:05:58,209 INFO Looking at lp:libunity-webapps
2013-07-15 15:05:59,281 INFO Looking at lp:unity-webapps-deviantart
2013-07-15 15:05:59,843 INFO Looking at lp:unity-webapps-yandexmusic
2013-07-15 15:06:00,339 INFO Looking at lp:unity-webapps-amazon
2013-07-15 15:06:00,946 INFO Looking at lp:unity-webapps-vkcom
2013-07-15 15:06:01,648 INFO Looking at lp:unity-webapps-googlecalendar
2013-07-15 15:06:02,263 INFO Looking at lp:unity-webapps-googleplus
2013-07-15 15:06:03,228 INFO Looking at lp:unity-webapps-newsblur
2013-07-15 15:06:03,683 INFO Looking at lp:unity-webapps-deezer
2013-07-15 15:06:04,379 INFO Looking at lp:unity-webapps-lordofultima
2013-07-15 15:06:05,125 INFO Looking at lp:unity-webapps-wordpress
2013-07-15 15:06:06,307 INFO Looking at lp:unity-webapps-hulu-player
2013-07-15 15:06:06,812 INFO Looking at lp:unity-webapps-facebookmessenger
2013-07-15 15:06:07,583 INFO Looking at lp:unity-webapps-tiberiumalliances
2013-07-15 15:06:08,398 INFO Looking at lp:unity-webapps-launchpad
2013-07-15 15:06:08,939 INFO Looking at lp:unity-webapps-mail-ru
2013-07-15 15:06:09,525 INFO Looking at lp:unity-webapps-yahoomail
2013-07-15 15:06:10,107 INFO Looking at lp:unity-webapps-tumblr
2013-07-15 15:06:11,250 INFO Looking at lp:unity-webapps-librefm
2013-07-15 15:06:11,763 INFO Looking at lp:unity-webapps-subwayirc
2013-07-15 15:06:12,035 ERROR lp:unity-webapps-subwayirc not found
Traceback (most recent call last):
  File "./cu2d-check-stalled-mps", line 32, in <module>
    sys.exit(command(BASEDIR))
  File "../c2dconfigutils/cu2dWatchDog.py", line 109, in __call__
    default_config_path)
  File "../c2dconfigutils/cu2dWatchDog.py", line 96, in process_stacks
    threshold)
TypeError: can only concatenate list (not "NoneType") to list