perf tools: Still continue on failed parsing of an event

Even though an event may fail to parse, we should not kill the
entire report. The trace should still be able to show what it
can.

If an event fails to parse, a warning is printed, and the output
continues.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <20091014194359.190809589@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>