[sushi] font-widget: resync from gnome-font-viewer

[Cosimo Cecchi <cosimoc src gnome org>]

commit f7ce2b3ab585baeb687cb8133f5ab66843b6f855
Author: Cosimo Cecchi <cosimoc gnome org>
Date:   Sat Nov 21 14:25:49 2015 -0800

    font-widget: resync from gnome-font-viewer

 src/libsushi/sushi-font-widget.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/src/libsushi/sushi-font-widget.c b/src/libsushi/sushi-font-widget.c
index 1b7febd..3709db5 100644
--- a/src/libsushi/sushi-font-widget.c
+++ b/src/libsushi/sushi-font-widget.c
@@ -636,7 +636,8 @@ sushi_font_widget_draw (GtkWidget *drawing_area,
 
   for (i = 0; i < n_sizes; i++) {
     cairo_set_font_size (cr, sizes[i]);
-    draw_string (self, cr, padding, self->priv->sample_string, &pos_y);
+    if (self->priv->sample_string !=  NULL)
+      draw_string (self, cr, padding, self->priv->sample_string, &pos_y);
     if (pos_y > allocated_height)
       break;
   }