CppEditor: Fix always-false-condition

The condition didn't make sense. tk.kind() can't be < T_FIRST_QT_KEYWORD
*and* tk.kind() > T_LAST_KEYWORD at the same time.

Change-Id: Id300ad84f37eeff5081b0389c00d574a9cb23f35
Reviewed-by: Orgad Shaneh <orgads@gmail.com>