telit: fix g_object_unref failed assertion
Fix the following g_object_unref failed assertion:
ModemManager[385967]: <debug> [1632924639.132023] [modem0/ttyUSB2/at] --> 'AT+CSIM=1<CR>'
ModemManager[385967]: <debug> [1632924639.144892] [modem0/ttyUSB2/at] <-- '<CR><LF>ERROR<CR><LF>'
ModemManager[385967]: <debug> [1632924639.145021] [modem0/ttyUSB2/at] operation failure: 100 (Unknown error)
(ModemManager:385967): GLib-GObject-CRITICAL **: 16:10:39.145: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Edited by Daniele Palmas