[FIX] menu: can open empty menu popover

[hokolomopo]

Description

Since the split of Menu and MenuPopover, we can open an empty menu, which is not desired.

Two issues:

• the t-if condition was plainly wrong, checking for the existence of the array rather than it's length.
• the logic to know what menus are visible or not was in the Menu component, but is needed in the parent MenuPopover component to know if we should open the popover or not.

Task: 5863077

review checklist

• feature is organized in plugin, or UI components
• support of duplicate sheet (deep copy)
• in model/core: ranges are Range object, and can be adapted (adaptRanges)
• in model/UI: ranges are strings (to show the user)
• undo-able commands (uses this.history.update)
• multiuser-able commands (has inverse commands and transformations where needed)
• new/updated/removed commands are documented
• exportable in excel
• translations (_t("qmsdf %s", abc))
• unit tested
• clean commented code
• track breaking changes
• doc is rebuild (npm run doc)
• status is correct in Odoo

[robodoo]