bug#52293: 29.0.50; [PATCH] Prevent further cases of duplicated separators in context menus

[Juri Linkov]

> Attached is a patch to fix this based on the discussion in bug#52237.

Thanks for the patch.

> One slightly odd thing is that for context menu functions that put their items
> at the top, they place their separator *below* the items. Other functions
> place the separator *above* the items.

There is some logic in this: when the menu doesn't contain a separator
at the top, then it is necessary to add a separator below the added items,
e.g. by modifying such a menu:

  - existing menu item 1
  - existing menu item 2

to

  - new item 1
  - new item 2
  - new separator
  - existing menu item 1
  - existing menu item 2