togglebutton: always set PRELIGHT state when in_button = TRUE

togglebutton: always set PRELIGHT state when in_button = TRUE

Previously, we would avoid setting the prelight state flag when
button_down was TRUE and draw_indicator = FALSE, which is the normal
case of a GtkToggleButton during a mouse press.
It looks like this behavior was introduced a long time ago with commit
b94e6c0a8036a0489ac8ca71de75ba7611218e50. I believe the reason was that
a widget in GTK2 couldn't have more than a single state (e.g.
hover+active) at a given moment.

https://bugzilla.gnome.org/show_bug.cgi?id=684038