[gtk+] scale: don't add scale label for empty markup

[Cosimo Cecchi <cosimoc src gnome org>]

commit b1144a73de8924bb83147526f86c69ed14240bfc
Author: Cosimo Cecchi <cosimoc gnome org>
Date:   Wed Mar 2 11:16:39 2016 -0800

    scale: don't add scale label for empty markup
    
    This is a regression from the gadget port.

 gtk/gtkscale.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtkscale.c b/gtk/gtkscale.c
index 33e5199..73c3f65 100644
--- a/gtk/gtkscale.c
+++ b/gtk/gtkscale.c
@@ -2018,7 +2018,7 @@ gtk_scale_add_mark (GtkScale        *scale,
                                NULL,
                                gtk_scale_render_mark_indicator,
                                mark, NULL);
-  if (mark->markup)
+  if (mark->markup && *mark->markup)
     mark->label_gadget =
       gtk_css_custom_gadget_new ("label",
                                  GTK_WIDGET (scale), mark->gadget,