process_one catches wrong QueueEmpty exception type

[jeffyjefflabs]

The process_one function catches asyncio.QueueEmpty, but msg_queue is a tornado Queue and get_nowait raises its own QueueEmpty type, not the one in asyncio. This looks like it was part of the native async refactor for ipykernel 6, so I don't know if it's as simple as changing what type is caught, or if some other change needs to be made.

ipykernel 6.2, tornado 6.1