tools lib traceevent: Set int_array fields to NULL if freeing from error

tools lib traceevent: Set int_array fields to NULL if freeing from error

Had a bug where on error of parsing __print_array() where the fields are
freed after they were allocated, but since they were not set to NULL,
the freeing of the arg also tried to free the already freed fields
causing a double free.

Fix process_hex() while at it.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20160209204237.188327674@goodmis.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>