parse-events: Let pevent_free() take a NULL pointer
parse-events: Let pevent_free() take a NULL pointer

The pevent_free() should ack like other free()s and allow a
NULL pointer to be passed to it which makes error handling a bit
easier for the users of pevent_free().

Signed-off-by: Steven Rostedt <43232e92d70cc7aa53504ad0397085ee47bad87f@goodmis.org>

bigzz/trace-cmd,bigzz/trace-cmd