Sometimes we're segfaulting because we were expecting that the
perf_sample.raw_data field was set as requested, but in some cases
that needs further investigation, that field can be NULL, leading
to segfaults.

Make the tool more robust by checking that before calling any per event
handlers that may try to use that field.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
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-g1fmodl6ys4lq8honbj1igoi@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>