gpiod.h: documentation updates
gpiod.h: documentation updates

Clarify that all functions dealing with sets of lines expect at least
a single line in order to work correctly and that the behavior is
undefined for zero lines. This applies both to bulk objects as well
as the high-level API.

Signed-off-by: Bartosz Golaszewski <108de5fbc428215dc26df4468b48691526611148@gmail.com>

brgl/libgpiod,brgl/libgpiod,brgl/libgpiod,brgl/libgpiod