genapic broke early safe_smp_processor_id(), especially when you got a
WARN_ON or oops early it would loops forever in show_trace.  The reason was
that the x86_cpu_to_apicid array wasn't correctly initialized.

This patch fixes this by just testing for this case.

Orginally from James Cleverdon
Acked-by: Andi Kleen <ak@muc.de> 
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>