Fix bug of mal-structured dup group - When a user changes tween type of a tween, the structure of dup group may not satisfy the requirement of new type. - It causes unexpected behavior. - It is fixed by checking structure and remove mal-structured ones.

<project>
	<scene src='list.mbsvg' />
	<source src='main.c'/>
	<source src='%n.c'/>
	<source src='%n.h'/>
	<source src='Makefile'/>
</project>