UI: Fix Support for Anonymous Menu Separators

Re-enables support for menus to have items without identifier or name that can be used to separate sections.

Differential Revision: https://developer.blender.org/D9463

Reviewed by Hans Goudey

source/blender/editors/interface/interface.c

@@ -4261,8 +4261,8 @@ static void ui_def_but_rna__menu(bContext *UNUSED(C), uiLayout *layout, void *bu
                    0,
                    "");
         }
-        uiItemS(column);
       }
+      uiItemS(column);
     }
     else {
       if (item->icon) {