network: Catch errors when reading devices
NetworkManager added support for a new device - NMDeviceWifiP2P - but did not add the corresponding enum value in NMDeviceType. The return value for nm_device_get_device_type() is therefore "illegal" for the newly added device, and gjs throws an exception.
This should ultimately be fixed in libnm, but as errors when adding one device shouldn't interfere with adding any other devices, catching exception is a good idea anyway, so do just that.
Fixes #1023 (closed)