KVM: nSVM: Preserve IRQ/NMI/SMI priority irrespective of exiting behavior

Short circuit vmx_check_nested_events() if an unblocked IRQ/NMI/SMI is
pending and needs to be injected into L2, priority between coincident
events is not dependent on exiting behavior.

Fixes: b518ba9f ("KVM: nSVM: implement check_nested_events for interrupts")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>