PangoGlyphItem: Better treatment of ellipsized runs

When we reapply non-shape attributes, we must take care to
not add any attributes that start in the middle of an
ellipsized run, or we end up with a blue, underlined ellipsis
if there is a link anywhere inside the ellipsized text.

https://bugzilla.gnome.org/show_bug.cgi?id=735732