gtkcssprovider: Free shorthand border GValues in the right place

The call to gtk_border_free() within unpack_border() felt completely
in the wrong place, as the border actually pertains to the GValue
being unpacked. Plus, the GValue itself was also being leaked.

gtk/gtkcssprovider.c

@@ -1092,6 +1092,7 @@ gtk_css_ruleset_add (GtkCssRuleset          *ruleset,
           gtk_css_ruleset_add (ruleset, child, value);
         }
       g_free (parameters);
+      property_value_free (value);
       return;
     }
 

gtk/gtkstyleproperty.c

@@ -1187,8 +1187,6 @@ unpack_border (const GValue *value,
   g_value_init (&parameter[3].value, G_TYPE_INT);
   g_value_set_int (&parameter[3].value, border->right);
 
-  gtk_border_free (border);
-
   *n_params = 4;
   return parameter;
 }