bug#27717: other-window when there is no other window

[Eli Zaretskii]

> From: 積丹尼 Dan Jacobson
>       <jidanni@jidanni.org>
> Date: Sun, 16 Jul 2017 23:13:33 +0800
> Cc: 27717@debbugs.gnu.org
> 
> "In an interactive call, COUNT is the numeric prefix argument."
> 
> All I know is the user did C-x o, not C-u 0 C-x o.
> 
> So I would hope the program would distinguish the two.

If your ring has exactly one slot, then going to the next will end up
right where you started.  There's nothing odd about that, and no
special reason to signal an error or output a message.  You can
instantly know what happened without any message.