crash when the app send requests

A crash occurred when my app continued to send requests while the Network section was open
```
__71-[DBNetworkViewController networkDebugToolkit:didUpdateRequestAtIndex:]_block_invoke (DBNetworkViewController.m:210)
__29-[DBMainQueueOperation start]_block_invoke (DBMainQueueOperation.m:72)
```

DBDebugToolkit (0.6.0)
iOS 15.5
MacOS 12
Xcode 13.4.1