[libft] ft_lstadd_front memory leak

[iijung]

sample

t_list *old;  // 1 > 2 > 3
t_list *new; // a > b > c 

as-is

ft_lstadd_front(old, new);  // a > 1 > 2 > 3   (b, c memory leak)

to-be

ft_lstadd_front(old, new);  // a > b > c > 1 > 2 > 3   (no memory leak)

[iijung]

#43

[xicodomingues]

Answered in the pull request.