GSM indicator does not work if phosh is started with no ModemManager running
To reproduce:
sudo systemctl disable --now ModemManager
# the GSM indicator disappears
sudo systemctl restart phosh
# there's no GSM indicator, as expected
sudo systemctl enable --now ModemManager
# no GSM indicator appears, even though it should
Just restarting ModemManager with GSM indicator already working does not trigger this bug.