Crash on mm_log_object_get_id

Related to #423 (closed).

This is a new stack trace -

Thread 0 (id: 0x00000902)
Exception infoSIGSEGV /0x00000000 @0x00000010
0x00005b3889e27c4a	(ModemManager -mm-log-object.c:65)		mm_log_object_get_id
0x00005b3889e27f24	(ModemManager -mm-log.c:256)		_mm_log
0x00005b3889e090b4	(ModemManager -mm-broadband-modem-mbim.c:2358)		mbim_device_removed_cb
0x00007b39a3ba1fdc	(libgobject-2.0.so.0 -gclosure.c:873)		_g_closure_invoke_va
0x00007b39a3bb56bb	(libgobject-2.0.so.0 -gsignal.c:3406)		g_signal_emit_valist
0x00007b39a3bb60ba	(libgobject-2.0.so.0 -gsignal.c:3553)		g_signal_emit
0x00007b39a3d2d85d	(libmbim-glib.so.4 -mbim-device.c:1065)		data_available
0x00007b39a3b3b536	(libglib-2.0.so.0 -gmain.c:3337)		g_main_context_dispatch
0x00007b39a3b3b841	(libglib-2.0.so.0 -gmain.c:4131)		g_main_context_iterate
0x00007b39a3b3babd	(libglib-2.0.so.0 -gmain.c:4329)		g_main_loop_run
0x00005b3889d9baf0	(ModemManager -main.c:216)		main
0x00007b39a38dfe04	(libc.so.6 + 0x00022e04)		__libc_start_main
0x00005b3889d9b909	(ModemManager + 0x00057909)		_start
0x00007ffe6494d627