fix(modules/nic): handle missing wireless strength info gracefully

if unable to read wireless signal strength -> show an error

fixes #1029

bumblebee_status/modules/core/nic.py

@@ -22,6 +22,7 @@
 import shutil
 import netifaces
 import subprocess
+import os
 
 import core.module
 import core.decorators
@@ -177,6 +178,8 @@ def get_ssid(self, intf):
     def get_strength_dbm(self, intf):
         if not self._iswlan(intf) or self._istunnel(intf) or not self.iw:
             return None
+        if not os.path.isfile("/proc/net/wireless"):
+            return None
 
         with open("/proc/net/wireless", "r") as file:
             for line in file: