attr_filter segfault

[Alan DeKok]

Alexander Clouter wrote:
> Only me...again doing things I probably should not do with FreeRADIUS.

  It shouldn't crash...

> So I decided to slap in unwisely placed 'handled' and the attr_filter on 
> the proxying server (in post-proxy) exploded.  The backtrace is below 
> and I also slipped in a 'detail' and can see that the attribute value is 
> pretty borked for 'Freeradius-Proxied-To'.

  It exploded because there was no proxy reply packet.  And it didn't
check for that case.

  I've committed a fix.  If there's no proxy reply packet, it will
return noop.

  Alan DeKok.