After applying the patch in bug 119891, an assertion fails when I remove a
non-spacing mark in gedit.  This is what I get when I remove a mark in gedit:

(gedit:1327): GtkSourceView-CRITICAL **: file gtksourceundomanager.c: line 617
(gtk_source_undo_manager_insert_text_handler): assertion `strlen (text) ==
(guint)length' failed

And if I undo, I get both the mark *and a copy of it's base character* inserted,
resulting in two base characters, which is wrong.

For example, say I have this:

بهِداد

and I remove the Kasre mark, I get:

بهداد

and Undo and get:

بهِهداد

Should be easy to fix though.