settings: don't add non-existant key in raw xy processing

lib/logitech_receiver/settings.py

@@ -1448,6 +1448,7 @@ class RawXYProcessing:
 
     def start(self, key):
         device_key = next((k for k in self.device.keys if k.key == key), None)
+        if device_key:
             self.keys.append(device_key)
             if not self.active:
                 self.active = True