Exception occurred in Group control

Issue:
When components are destroyed dynamically in side a group control,
exception observed inside the activeChanged function.

Fix:
checking whether the component is destroyed or not.

Enyo-DCO-1.1-Signed-off-by: Srinivas V srinivas.v@lge.com
Merge pull request #842 from enyojs/BHV-13593-srinvasv

Exception occurred in Group control