Ensure Progress default value is -1

[philippjfr]

Fixes #3166

[codecov]

Codecov Report

Merging #3307 (9e5cb6a) into master (6895a63) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3307      +/-   ##
==========================================
+ Coverage   83.40%   83.41%   +0.01%     
==========================================
  Files         196      196              
  Lines       26495    26502       +7     
==========================================
+ Hits        22097    22106       +9     
+ Misses       4398     4396       -2     

Impacted Files	Coverage Δ
panel/widgets/indicators.py	92.48% <100.00%> (+0.33%)	⬆️
panel/widgets/tables.py	87.88% <0.00%> (-0.04%)	⬇️
panel/reactive.py	77.60% <0.00%> (+0.22%)	⬆️

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