[libsmi] bug in libsmi-0.2.17

Hi,

The following code and MIB results in a SIGSEGV from libsmi if the IMPORTed MIBs are unavailable. The offending code is check.c:933 which attempts to dereference object->typePtr which is NULL. I don't know the code well enough to produce a sensible patch.

Regards,

Damian.