Just fall back to resetting those fields, if set, warning the user that
that feature is not available.

If guest samples appear they will just be discarded because no struct
machine will be found and thus the event will be accounted as not
handled and dropped, see 0c095715.
Reported-by: Namhyung Kim <namhyung@gmail.com>
Tested-by: Joerg Roedel <joerg.roedel@amd.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Joerg Roedel <joerg.roedel@amd.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-vuwxig36mzprl5n7nzvnxxsh@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>