closing OcrdBrowser causes exception

[bertsky]

After closing the OcrdBrowser window in the web interface, I always get an exception on the log view:

websockets.exceptions.ConnectionClosedError: no close frame received or sent
ERROR:asyncio:Future exception was never retrieved
future: <Future finished exception=ConnectionClosedError(None, None, None)>
Traceback (most recent call last):
  File "/usr/local/ocrd-monitor/.venv/lib/python3.11/site-packages/websockets/legacy/protocol.py", line 963, in transfer_data
    message = await self.read_message()
              ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/ocrd-monitor/.venv/lib/python3.11/site-packages/websockets/legacy/protocol.py", line 1033, in read_message
    frame = await self.read_data_frame(max_size=self.max_size)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/ocrd-monitor/.venv/lib/python3.11/site-packages/websockets/legacy/protocol.py", line 1108, in read_data_frame
    frame = await self.read_frame(max_size)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/ocrd-monitor/.venv/lib/python3.11/site-packages/websockets/legacy/protocol.py", line 1165, in read_frame
    frame = await Frame.read(
            ^^^^^^^^^^^^^^^^^
  File "/usr/local/ocrd-monitor/.venv/lib/python3.11/site-packages/websockets/legacy/framing.py", line 68, in read
    data = await reader(2)
           ^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/asyncio/streams.py", line 748, in readexactly
    raise exceptions.IncompleteReadError(incomplete, n)
asyncio.exceptions.IncompleteReadError: 0 bytes read on a total of 2 expected bytes

The above exception was the direct cause of the following exception:

websockets.exceptions.ConnectionClosedError: no close frame received or sent
ERROR:asyncio:Future exception was never retrieved
future: <Future finished exception=ConnectionClosedError(None, None, None)>
Traceback (most recent call last):
  File "/usr/local/ocrd-monitor/.venv/lib/python3.11/site-packages/websockets/legacy/protocol.py", line 963, in transfer_data
    message = await self.read_message()
              ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/ocrd-monitor/.venv/lib/python3.11/site-packages/websockets/legacy/protocol.py", line 1033, in read_message
    frame = await self.read_data_frame(max_size=self.max_size)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/ocrd-monitor/.venv/lib/python3.11/site-packages/websockets/legacy/protocol.py", line 1108, in read_data_frame
    frame = await self.read_frame(max_size)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/ocrd-monitor/.venv/lib/python3.11/site-packages/websockets/legacy/protocol.py", line 1165, in read_frame
    frame = await Frame.read(
            ^^^^^^^^^^^^^^^^^
  File "/usr/local/ocrd-monitor/.venv/lib/python3.11/site-packages/websockets/legacy/framing.py", line 68, in read
    data = await reader(2)
           ^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/asyncio/streams.py", line 748, in readexactly
    raise exceptions.IncompleteReadError(incomplete, n)
asyncio.exceptions.IncompleteReadError: 0 bytes read on a total of 2 expected bytes

The above exception was the direct cause of the following exception:

websockets.exceptions.ConnectionClosedError: no close frame received or sent
WARNING:root:Could not find process with ID 118
WARNING:root:Could not find process with ID 121
INFO:     172.16.4.79:51198 - "GET /workspaces/ HTTP/1.1" 200 OK
INFO:     connection closed

(The Monitor is still usable, but the exception is uncanny...)