check item_proxy attribute before calling - sni_system_tray

[t-gitt]

not sure why this happens. But it was preventing my tray to load. Added some checks so that it can have a safe fallback and not break if this item_proxy doesn't have these attributes.

related to #224

[nwg-piotr]

related to #224

Does it resolve the Discord icon missing issue on your side? I only see a blank space in the place where the icon should be.

[t-gitt]

I don't use Discord. I only have my bluetooth manager tray (which was not shown before this pr fix as the tray module was breaking).
I installed discord, I also can't see its tray icon.

When I did this I added a breakpoint item.py:60 so here are some variables values. Maybe they will help you in debugging, maybe this dasbus library was updated or something.

self.__dict__
{'service_name': ':1.714', 'object_path': '/org/blueman/sni', 'on_loaded_callback': <bound method StatusNotifierHostInterface.item_loaded_handler of <nwg_panel.modules.sni_system_tray.host.StatusNo
tifierHostInterface object at 0x7f9647eb3450>>, 'on_updated_callback': <bound method StatusNotifierHostInterface.item_updated_handler of <nwg_panel.modules.sni_system_tray.host.StatusNotifierHostInterface object
 at 0x7f9647eb3450>>, 'session_bus': <dasbus.connection.SessionMessageBus object at 0x7f9647eb2dd0>, 'properties': {'ItemIsMenu': True}, 'item_proxy': <dasbus.client.proxy.ObjectProxy object at 0x7f9647e77380>, 
'item_observer': DBusObserver(:1.714)}                         
                                                                                                                                                    
self.item_proxy
<dasbus.client.proxy.ObjectProxy object at 0x7f9647e77380>
                                                                                                                                    
self.item_proxy.__dir__()
['__module__', '__doc__', '__slots__', '_locals', '__init__', '_get_interface', '_interface_names', '__abstractmethods__', '_abc_impl', '_get_member', '_create_member', '__getattr__', '
__setattr__', '_handler', '_lock', '_members', '__weakref__', '__new__', '__repr__', '__hash__', '__str__', '__getattribute__', '__delattr__', '__lt__', '__le__', '__eq__', '__ne__', '__gt__', '__ge__', '__reduc
e_ex__', '__reduce__', '__getstate__', '__subclasshook__', '__init_subclass__', '__format__', '__sizeof__', '__dir__', '__class__']                                                                                

self.item_proxy._interface_names
{'ItemIsMenu': 'org.kde.StatusNotifierItem', 'Menu': 'org.kde.StatusNotifierItem', 'ToolTip': 'org.kde.StatusNotifierItem', 'Title': 'org.kde.StatusNotifierItem', 'Status': 'org.
kde.StatusNotifierItem', 'IconName': 'org.kde.StatusNotifierItem', 'Id': 'org.kde.StatusNotifierItem', 'Category': 'org.kde.StatusNotifierItem', 'NewToolTip': 'org.kde.StatusNotifierItem', 'NewStatus': 'org.kde.
StatusNotifierItem', 'NewIcon': 'org.kde.StatusNotifierItem', 'Activate': 'org.kde.StatusNotifierItem', 'PropertiesChanged': 'org.freedesktop.DBus.Properties', 'Set': 'org.freedesktop.DBus.Properties', 'GetAll':
 'org.freedesktop.DBus.Properties', 'Get': 'org.freedesktop.DBus.Properties', 'GetMachineId': 'org.freedesktop.DBus.Peer', 'Ping': 'org.freedesktop.DBus.Peer', 'Introspect': 'org.freedesktop.DBus.Introspectable'
}