BUG: Check that region for thread is not empty

Fix the following failure on ITKExamples:

  http://open.cdash.org/testDetails.php?test=199789893&build=2975061

Change-Id: I8b67c0d4e38a688154d0c9a316b491a7a2949f79
Merge topic 'FixObserveExample'

82f1d19 BUG: Check that region for thread is not empty