Return an appropriate GtkStyle from gtk_rc_get_style_by_paths()

Return an appropriate GtkStyle from gtk_rc_get_style_by_paths()

Always returning NULL (no match) from gtk_rc_get_style_by_paths()
means that looking up colors and style properties based on the
GtkStyle will give default values instead of themed values. We can
do better by returning a GtkStyle based on a GtkWidgetPath that we
figure out from the values passed in to get_style_by_paths().

https://bugzilla.gnome.org/show_bug.cgi?id=637520