[gtk+] symboliccolor: fix a critical warning

[Cosimo Cecchi <cosimoc src gnome org>]

commit a2bef8ca516f5e9335c1133c902185e85fa66e3d
Author: Cosimo Cecchi <cosimoc gnome org>
Date:   Fri Sep 28 12:49:22 2012 -0400

    symboliccolor: fix a critical warning
    
    This was introduced in 0cc32eae6219599882e7dc75115050ce77607887

 gtk/gtksymboliccolor.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtksymboliccolor.c b/gtk/gtksymboliccolor.c
index e68eb91..53409f1 100644
--- a/gtk/gtksymboliccolor.c
+++ b/gtk/gtksymboliccolor.c
@@ -740,7 +740,7 @@ _gtk_symbolic_color_resolve_full (GtkSymbolicColor        *color,
   GtkCssValue *value;
 
   g_return_val_if_fail (color != NULL, FALSE);
-  g_return_val_if_fail (GTK_IS_STYLE_PROVIDER_PRIVATE (provider), FALSE);
+  g_return_val_if_fail (provider == NULL || GTK_IS_STYLE_PROVIDER_PRIVATE (provider), FALSE);
   g_return_val_if_fail (current != NULL, FALSE);
 
   if (dependencies == NULL)