Only newly created inset were entered everytime.
* Derived classes of CommandInset do not draw all cells, so return false.
(fixes http://bugzilla.lyx.org/show_bug.cgi?id=3715)
git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@18742 a592a061-630c-0410-9148-cb99ea01b6c8