Fix for removal of orphaned node (#532)

Author: marcelveldt

matter_server/server/device_controller.py

@@ -642,7 +642,9 @@ async def remove_node(self, node_id: int) -> None:
             0,
             Clusters.OperationalCredentials.Attributes.CurrentFabricIndex,
         )
-        fabric_index = node.attributes[attribute_path]
+        fabric_index = node.attributes.get(attribute_path)
+        if fabric_index is None:
+            return
         result: Clusters.OperationalCredentials.Commands.NOCResponse | None = None
         try:
             result = await self.chip_controller.SendCommand(