Changes

global_platform/scp: mapdu may be undeclared

when we sign and encrypt the APDU in _wrap_cmd_apdu (SCP03) we return an "mapdu"
at the end. However, in the (unlikely?) case where self.do_cencand
self.do_cmac are false, mapdu will be undeclared. In _wrap_cmd_apdu for SCP02
we just re-use the apdu variable and return it at the end, so when no
encryption and no signing is applied, the APDU falls just through without any
modifications. We should have the same mechanism for the SCP03 wrapping as
well.

Related: OS#6367

Change-Id: Ic7089a69dffd7313572c5b3e5953200be5925766