add forgotten const cast
add forgotten const cast

taglib/taglib,taglib/taglib,Distrotech/taglib,taglib/taglib,TsudaKageyu/taglib,Distrotech/taglib,TsudaKageyu/taglib,Distrotech/taglib,black78/taglib,black78/taglib,black78/taglib,TsudaKageyu/taglib