/// move up/down in a text inset, called for LFUN_UP/DOWN,
/// return true if successful, updateNeeded set to true if fullscreen
/// update is needed, otherwise it's not touched
/// move up/down in a text inset, called for LFUN_UP/DOWN,
/// return true if successful, updateNeeded set to true if fullscreen
/// update is needed, otherwise it's not touched