label: Avoid creating new attribute list

Only create an attribute list for merging if we actually need to merge.

This bug was introduced in 5230cfe805

gtk/gtklabel.c

@@ -3361,7 +3361,7 @@ gtk_label_ensure_layout (GtkLabel *label)
               pango_attr_list_insert (attrs, attribute);
             }
         }
-      else if (priv->markup_attrs || priv->attrs)
+      else if (priv->markup_attrs && priv->attrs)
         attrs = pango_attr_list_new ();
       else
         attrs = NULL;