BUG FIX: Set the last document content's DockPanel to null throws exception, due to GiveUpFocus tries to re-display the content again.
BUG FIX: Set the last document content's DockPanel to null throws exception, due to GiveUpFocus tries to re-display the content again.

git-svn-id: dea0e26cebe12643f3180c2c69384aa256c684b6@19 764a741f-c628-0410-a7dc-abe640748d39

yolanother/DockPanelSuite