//! List selection with viewport scrolling - helper functions
/// Wrap index forward (standalone function)
pubfnwrap_next(index:usize, len:usize)->usize{if len ==0{0}else{(index +1)% len
}}/// Wrap index backward (standalone function)
pubfnwrap_prev(index:usize, len:usize)->usize{if len ==0{0}elseif index ==0{
len -1}else{
index -1}}