talloc:documentation - explain that "talloc_free" works also with "NULL" pointers

talloc:documentation - explain that "talloc_free" works also with "NULL" pointers

(talloc.c)
...
> static inline int _talloc_free_internal(void *ptr, const char *location)
> {
>        struct talloc_chunk *tc;
>
>        if (unlikely(ptr == NULL)) {
>                return -1;
>        }
>
>        tc = talloc_chunk_from_ptr(ptr);
...

Obviously this never had been documented before.