spoolss: cache_key handle allocation failures early

spoolss: cache_key handle allocation failures early

On cache_key allocation failure, set_printer_hnd_name() currently
stumbles through the rest of the function, and includes extra logic to
handle a NULL key later on.
Handling the allocation failure early makes sense, and also allows for
the NULL key checks to be removed.

Signed-off-by: David Disseldorp <ddiss@samba.org>
Reviewed-by: Guenther Deschner <gd@samba.org>
Autobuild-User(master): Günther Deschner <gd@samba.org>
Autobuild-Date(master): Wed Apr 15 18:55:50 CEST 2015 on sn-devel-104