C++: Fix off-by-one in scopeAt.

The only Scope that set the end offset to *before* the last token
was ObjCClassDeclaration.

Change-Id: Icbdb5bcdd72d96087ac586ad51510fed74a633eb
Reviewed-on: http://codereview.qt.nokia.com/2820


Reviewed-by: Leandro T. C. Melo <leandro.melo@nokia.com>