Don't use Gtk.Widget.ensure_style()
Avoid empty body of conditional statement

Vala is warning about this now, and it makes the code a bit harder to
read.
Fix invalid GtkTextIter after inserting thousands separator

Ensure the iterator points to the position immediately after the
inserted text when insert_text() returns by using a mark with right
gravity.

Note that this may have been associated with the following crasher:

https://bugzilla.gnome.org/show_bug.cgi?id=737291