mmcli,output: skip printing empty value lists
E.g. we shouldn't print emergency numbers field if there is none available:
$ mmcli -i 0
-------------------------------
General | dbus path: /org/freedesktop/ModemManager1/SIM/0
-------------------------------
Properties | imsi: 901700000026890
| iccid: 8988211000000268907
| operator id: 90170
| operator name: 901 70
| emergency numbers:
Edited by Aleksander Morgado