Check for jupyter_client before patching event_loop on Windows

[hoxbro]

Fixes #3627 related to importing panel in the IPython startup folder.

[philippjfr]

Why partially?

[codecov]

Codecov Report

Merging #3770 (4f9e39d) into master (4f8ab43) will increase coverage by 0.00%.
The diff coverage is 66.66%.

@@           Coverage Diff           @@
##           master    #3770   +/-   ##
=======================================
  Coverage   83.57%   83.57%           
=======================================
  Files         214      214           
  Lines       31348    31367   +19     
=======================================
+ Hits        26198    26215   +17     
- Misses       5150     5152    +2     

Flag	Coverage Δ
ui-tests	33.85% <0.00%> (-0.02%)	⬇️
unitexamples-tests	76.46% <66.66%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
panel/io/server.py	76.59% <66.66%> (+0.02%)	⬆️
panel/widgets/tables.py	89.16% <0.00%> (ø)
panel/command/serve.py	37.11% <0.00%> (+0.39%)	⬆️
panel/config.py	60.22% <0.00%> (+0.55%)	⬆️
panel/io/document.py	66.37% <0.00%> (+1.24%)	⬆️

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[hoxbro]

It does not fix IndexError: pop from an empty deque, but I can see in the thread that this is not related to panel.

[philippjfr]

Thanks @hoxbro!