ReaderRolling: fix marker sometimes not removed
ReaderRolling: fix marker sometimes not removed

Noticed when jump to a footnote and quickly going back.

koreader/koreader,Frenzie/koreader,poire-z/koreader,NiLuJe/koreader,poire-z/koreader,NiLuJe/koreader,Frenzie/koreader,koreader/koreader