trace-cmd: Handle junk on last page for tracecmd_read_cpu_last()
trace-cmd: Handle junk on last page for tracecmd_read_cpu_last()

If the last page (or last pages) have just junk on it (timestamps
and discarded events), tracecmd_read_cpu_last should not return NULL.
It needs to test previous pages.

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

bigzz/trace-cmd,bigzz/trace-cmd