parse-events: Allow pevent_read_number_field() to have NULL field
parse-events: Allow pevent_read_number_field() to have NULL field

Let pevent_read_number_field() have a NULL field. Just return -1
if one does not exist.

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

bigzz/trace-cmd,bigzz/trace-cmd