bug#22490: 24.5; (newline 0) fails when point not after newline

[Eli Zaretskii]

> From: Dan Torop <dant@pnym.net>
> Date: Fri, 29 Jan 2016 13:46:47 -0500
> 
> The function "newline" with an argument of 0 will fail unless called
> when the character before the point is a newline. To test, start a new
> Emacs session, type space, then evaluate "(newline 0)". It should
> fail with a backtrace:
> 
> Debugger entered--Lisp error: (cl-assertion-failed (eq 10
> (char-before)))

Thanks, I fixed this for the upcoming Emacs 25.1.