Disallow 0x0000 as a PAN ID

The probability of it being randomly picked is about 0.002%

Author: puddly

zigpy_znp/zigbee/application.py

@@ -362,7 +362,7 @@ async def form_network(self):
         network_key = self.config[conf.CONF_NWK][conf.CONF_NWK_KEY]
 
         if pan_id is None:
-            pan_id = random.SystemRandom().randint(0x0000, 0xFFFE + 1)
+            pan_id = random.SystemRandom().randint(0x0001, 0xFFFE + 1)
 
         if extended_pan_id is None:
             extended_pan_id = ExtendedPanId(os.urandom(8))