libtirpc: missing NULL pointer checks
libtirpc: missing NULL pointer checks

This patch fixes various unexpected segfaults caused by
invoking rpcb_* functions with NULL arguments.

Signed-off-by: Steve Dickson <305cc9d5027c0f4e08c2697d4cabde07a8221669@redhat.com>

Distrotech/libtirpc,Distrotech/libtirpc,Distrotech/libtirpc