perf session: Dont queue events w/o timestamps

If the event has no timestamp assigned then the parse code sets it to
~0ULL which causes the ordering code to enqueue it at the end.

Process it right away.

Reported-by: Ian Munsie <imunsie@au1.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ian Munsie <imunsie@au1.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20101207124550.528788441@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>