bug#21602: 25.0.50; coding system seg fault

[Eli Zaretskii]

> From: Andreas Schwab <schwab@linux-m68k.org>
> Cc: 21602@debbugs.gnu.org,  rms@gnu.org
> Date: Sat, 03 Oct 2015 14:14:43 +0200
> 
> That still misses a few checks, and left some redundant checks.  I think
> it is better to put the checks in coding_inherit_eol_type, that will
> cover almost all cases.

I added the checks in coding_inherit_eol_type, but I think it's better
to keep the ones we already have.  In general, the sooner we detect
invalid arguments the better, especially when we are using a large
number of defaults of of many kinds, something the user might not be
aware of.

Thanks.