Fix Widget.from_param when precedence is negative

[philippjfr]

Fixes #3187

[codecov]

Codecov Report

Merging #3199 (f00a8aa) into master (4ae7887) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3199      +/-   ##
==========================================
- Coverage   82.99%   82.98%   -0.01%     
==========================================
  Files         193      193              
  Lines       25626    25637      +11     
==========================================
+ Hits        21268    21276       +8     
- Misses       4358     4361       +3     

Impacted Files	Coverage Δ
panel/tests/widgets/test_base.py	100.00% <100.00%> (ø)
panel/widgets/base.py	94.73% <100.00%> (+0.07%)	⬆️
panel/io/reload.py	69.23% <0.00%> (-2.20%)	⬇️
panel/tests/pane/test_plotly.py	98.15% <0.00%> (-0.62%)	⬇️

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