Ensure styling empty DataFrame does not error

[philippjfr]

Fixes #4022

[codecov]

Codecov Report

Merging #4028 (0b33225) into master (9c819d0) will increase coverage by 9.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4028      +/-   ##
==========================================
+ Coverage   74.65%   83.66%   +9.00%     
==========================================
  Files         223      223              
  Lines       33148    33144       -4     
==========================================
+ Hits        24748    27730    +2982     
+ Misses       8400     5414    -2986     

Flag	Coverage Δ
ui-tests	37.59% <22.22%> (?)
unitexamples-tests	74.67% <100.00%> (+0.01%)	⬆️

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

Impacted Files	Coverage Δ
panel/tests/widgets/test_tables.py	99.66% <100.00%> (+<0.01%)	⬆️
panel/widgets/tables.py	87.94% <100.00%> (+1.16%)	⬆️
panel/io/reload.py	69.56% <0.00%> (-2.18%)	⬇️
panel/tests/command/test_serve.py	83.95% <0.00%> (-1.42%)	⬇️
panel/io/cache.py	82.14% <0.00%> (-0.45%)	⬇️
panel/io/server.py	74.47% <0.00%> (-0.20%)	⬇️
panel/template/base.py	76.45% <0.00%> (-0.19%)	⬇️
panel/io/state.py	69.70% <0.00%> (-0.17%)	⬇️
panel/io/jupyter_server_extension.py	0.00% <0.00%> (ø)
panel/param.py	87.22% <0.00%> (+0.15%)	⬆️
... and 38 more

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more