[UX] Download dictionary: keep menu open (#4412)
[UX] Download dictionary: keep menu open (#4412)

As suggested by @poire-z in https://github.com/koreader/koreader/pull/4401#issuecomment-447629244
poire-z/koreader,mihailim/koreader,koreader/koreader,houqp/koreader,Frenzie/koreader,pazos/koreader,Hzj-jie/koreader,koreader/koreader,poire-z/koreader,NiLuJe/koreader,Markismus/koreader,Frenzie/koreader,mwoz123/koreader,NiLuJe/koreader