_gtk_icon_helper_draw: get style earlier

_gtk_icon_helper_draw: get style earlier

After checking for rendered_surface, the call to gtk_css_node_get_style
can invalidate the style and result in rendered_surface being set to
NULL. This was result in some icon views appearing blank on
Endless OS on armv7hl, and this error:

Gtk-CRITICAL **: gtk_css_style_render_icon_surface: assertion 'surface != NULL' failed

Call gtk_css_node_get_style earlier to ensure we always pass a valid
surface to gtk_css_style_render_icon_surface.

https://bugzilla.gnome.org/show_bug.cgi?id=765649
https://phabricator.endlessm.com/T13524