In apic_accept_pic_intr(), reject PIC interruptions if a i8259 PIC has
not been instantiated (isa_pic == NULL).
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sergio Lopez <slp@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>