Fix bug #3997: RTL paragraphs are painted slightly too far to the left

Fix bug #3997: RTL paragraphs are painted slightly too far to the left

In the computation of the row width, the last space on a row was included. However, this space is not drawn on screen and shouldn't contribute to the width. As a result all rows in a paragraph were painted slightly too far to the left, except the last on.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@30967 a592a061-630c-0410-9148-cb99ea01b6c8