Make the scrolling for large insets more naturally (bug #7662)

Make the scrolling for large insets more naturally (bug #7662)

The patch fixes a case that I had forgotten. Namely, the case that when the height of a row was larger than the height of the screen and that the cursor is already visible. That's why I added a new if case to catch all situations in which the row height is larger than the height of the screen. If we then need scrolling we scroll to height/4 and 3*height/4. In the end, the height_/4 and 3*height_/4 should be replaced by the rowheights in the inset, but we need some extra infrastructure for that.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@39697 a592a061-630c-0410-9148-cb99ea01b6c8