touchmenu: fix menu height calculation
touchmenu: fix menu height calculation

Markismus/koreader,NiLuJe/koreader,chihyang/koreader,apletnev/koreader,Frenzie/koreader,koreader/koreader,Frenzie/koreader,NickSavage/koreader,mihailim/koreader,lgeek/koreader,NiLuJe/koreader,frankyifei/koreader,mwoz123/koreader,koreader/koreader,poire-z/koreader,Hzj-jie/koreader,robert00s/koreader,houqp/koreader,poire-z/koreader,pazos/koreader