TextBoxWidget: fix crash when empty last line and alignment center/right (#5691)
TextBoxWidget: fix crash when empty last line and alignment center/right (#5691)


mihailim/koreader,mwoz123/koreader,Markismus/koreader,poire-z/koreader,Frenzie/koreader,koreader/koreader,NiLuJe/koreader,koreader/koreader,Hzj-jie/koreader,pazos/koreader,Frenzie/koreader,NiLuJe/koreader,poire-z/koreader