Core/Guild: Don't allow players to view officer notes without proper rights

Just a minor exploit, officer notes can be accessed by GetGuildRosterInfo() even if the player doesn't have the rights to do so.
From WoWWiki: "Returns the character's officer note if one exists, returns "" if there is no note or the current player does not have access to the officer notes"

::HandleRoster should not be called without a proper session (in order to broadcast), because we need to check individual players whether they have the rights. TC currently doesn't call it with NULL value to broadcast.