SystemInformation: Do not dereference NULL ifa_addr

From "man getifaddrs":

 "This means ifa_addr and other fields can actually be NULL if the
  interface has no address..."

Reported-by: Kornel Benko <kornel@lyx.org>
Change-Id: I9d9ad3ae9fb50cbcab46fa8c06b270e4c56c288e