button: Don't care about sizing if no child is set

We don't need to care in this case since the default values should
always be assumed to be 0, and setting a baseline of 0 is just wrong
when orientation == HORIZONTAL, it should be -1 (or unset).

gtk/gtkbutton.c

@@ -931,15 +931,6 @@ gtk_button_measure_ (GtkWidget      *widget,
                            minimum, natural,
                            minimum_baseline, natural_baseline);
     }
-  else
-    {
-      *minimum = 0;
-      *natural = 0;
-      if (minimum_baseline)
-        *minimum_baseline = 0;
-      if (natural_baseline)
-        *natural_baseline = 0;
-    }
 }
 
 /**