fix(class): fixed private access in method calls

[deFuzz77]

I created issue (#549) about not expecting value from private table. Commit dcdfe6e partially fixed this, but it creates a new issue.

Now, class documentation has one error, actually jesse.private.year returns 3, not nill.

-- code from https://overextended.dev/ox_lib/Modules/Class/Shared#example

CreateThread(function()
    local jesse = Student:new('Jesse', 2)
 
    jesse:introduceSelf() -- Hi! I'm Jesse, and I'm in year 2.
    jesse:setYear(3)
    jesse:introduceSelf() -- Hi! I'm Jesse, and I'm in year 3.
    print(jesse.private.year) -- nil  [now, this returns 3, not nil]
    print(getmetatable(jesse.private)) -- private
    jesse.private.year = 4 -- error
end)

I solve this with this simple if statement, and it works fine:

  __index = function(self, index)
      local di = getinfo(2, 'n')
  
      if di.namewhat ~= 'method' and di.namewhat ~= '' then return end
  
      return private[index]
  end,