bug#17560: 24.4.50; wrong type argument if rmail-delete-after-output set

[Eli Zaretskii]

> From: Ken Olum <kdo@cosmos.phy.tufts.edu>
> Date: Fri, 23 May 2014 11:02:18 -0400
> 
> Under a recent change, rmail-delete-forward takes an optional repeat
> count.  If not specified, the count defaults to nil, giving an error.
> This function is called with no arguments in several places including
> rmail-output (if rmail-delete-after-output is set).

Could you perhaps suggest a patch to fix this?  TIA.