ensure we do not emit to relay if disconnected

nicegui/air.py

@@ -138,4 +138,5 @@ class Air:
         await self.relay.disconnect()
 
     async def emit(self, message_type: str, data: Dict[str, Any], room: str) -> None:
-        await self.relay.emit('forward', {'event': message_type, 'data': data, 'room': room})
+        if self.relay.connected:
+            await self.relay.emit('forward', {'event': message_type, 'data': data, 'room': room})