bug#38384: (next|previous)-buffer silent about not switching

[Eli Zaretskii]

> From: Juanma Barranquero <lekktu@gmail.com>
> Date: Tue, 26 Nov 2019 13:08:12 +0100
> 
> In some circumstances, next-buffer and previous-buffer do not have any buffer 
> to switch to, and in that case
> they silently do nothing.  (Strictly speaking, they call 
> switch-to-(next|prev)-buffer, which do nothing and return
> nil).
> 
> I think they should throw a user-error, to inform the user about the 
> situation.

Could that disrupt noninteractive calls?