Fix Perspective Filter Errors

[MarcSkovMadsen]

I noticed at work that when I drag a column to the "Filter" it raises errors.

I can see its because the fix applied to the _process_property_change in #2300 needs to be applied to the _process_param_change method as well.

Because of #2518 I'm not able to show the behaviour before and after this fix is applied

@philippjfr . Is it possible to get this in Panel 0.12?

[codecov]

Codecov Report

Merging #2521 (ae2480f) into master (3de416e) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2521      +/-   ##
==========================================
+ Coverage   83.30%   83.31%   +0.01%     
==========================================
  Files         184      184              
  Lines       23186    23186              
==========================================
+ Hits        19314    19317       +3     
+ Misses       3872     3869       -3     

Impacted Files	Coverage Δ
panel/pane/perspective.py	54.14% <100.00%> (ø)
panel/tests/pane/test_plotly.py	98.73% <0.00%> (+0.63%)	⬆️
panel/io/reload.py	66.66% <0.00%> (+2.29%)	⬆️

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