NGmenus()
 Returns the number of 'Top Row' Menus
------------------------------------------------------------------------------

 Function:      NGmenus()

 Syntax:        NGmenus() --> nMenuCount

 Description:   NGmenus() returns the number of Menus one can find
                at the 'Top' Row. typically this would be between 1 and 3,
                but can theoritically be up to 10. If this function returns 0,
                it means the guide has no Menu choices, but rather consists
                of only one Short List, of Long entry. That entry
                can then be found at NG adres 378.

 Returns:       A number indicating the number of 'Menus'.
                When 0 is returned, then the first Long or Short List entry
                is located at Entry 378, so it's a bit tricky there.
                Otherwise, you just use the NGmenu????() functions. That is
                because the guide does not contain any menus but consists
                of a single Short Entry or Long Entry.

                The way to go would be to test NGtype(378), and accordingly
                handle the Short or Long Entry. Otherwise, use the
                NGmenu??() functions, and specifically the NGmenuEntry()
                function to acces the Norton Guide entries.