KVM: fix i8259 oops when no vcpus are online

If there are no vcpus, found will be NULL.  Check before doing anything with
it.
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/i8259.c

@@ -64,6 +64,9 @@ static void pic_unlock(struct kvm_pic *s)
 		if (!found)
 			found = s->kvm->bsp_vcpu;
 
+		if (!found)
+			return;
+
 		kvm_vcpu_kick(found);
 	}
 }