HU Editor: TU to existing LU action

[metas-lc]

Is this a bug or feature request?

bug
follow-up to #514

What is the current behavior?

move tu on existing LU allows you to put a tu on another tu or cu and you get errors

Which are the steps to reproduce?

1. go to HU Editor end select a random TU, use transform to put it on an existing LU
   => you can also select a TU. and if you select a TU, you get the following error
   "Ihr Test hat einen bisher unentdeckten Fehler offengelegt.
   ↵Bitte leiten Sie diese Meldung an metas weiter:↵↵Error: parentPIItem==null for parentHU=X_M_HU[M_HU_ID=1000031, Value=1000031, trxName=<>] and piOfChildHU=X_M_HU_PI[M_HU_PI_ID=2002659, Name=IFCO 6410, trxName=<>]"
   path:"/rest/api/process/ADP_540763/1007674/start"

2. same as last step, but CU on TU
   => Ihr Test hat einen bisher unentdeckten Fehler offengelegt.
   Bitte leiten Sie diese Meldung an metas weiter: Error: parentPIItem==null for parentHU=X_M_HU[M_HU_ID=1000058, Value=1000058, trxName=<>] and piOfChildHU=X_M_HU_PI[M_HU_PI_ID=2002659, Name=IFCO 6410, trxName=<>]

3. open hu editor from material receipt candidates with 100 LUs, with 1 TU each
   select a random TU and press on transform
   use action move tu on existing LU
   => you can also see the TUs (and if you select a TU you'll get a similar error like in steps 1 and 2)
   

What is the expected or desired behavior?

shall not be able to select TUs or CUs
shall not see TUs when you run move tu on existing LU

[metas-lc]

closing this task. to be fixed in #783