[Menusorter] Ignore warning for the plus_menu. (#3903)
[Menusorter] Ignore warning for the plus_menu. (#3903)

The plus_menu break the assumption of the menusorter about a tab beeing
always present.
See : https://github.com/koreader/koreader/pull/3844#issuecomment-383092219
Markismus/koreader,Hzj-jie/koreader,Frenzie/koreader,pazos/koreader,Frenzie/koreader,poire-z/koreader,NiLuJe/koreader,houqp/koreader,koreader/koreader,poire-z/koreader,mihailim/koreader,NiLuJe/koreader,mwoz123/koreader,koreader/koreader,lgeek/koreader