fix preprocess dispatch missing properties

[disberd]

The previous dispatch rules were sometimes missing the correct processing of Plotly properties when the Dict containing them was Dict{Any} rather than Dict{Symbol}.

Added an if inside the specific method to hopefully handle this. This might also trigger inside arbitrary data Dicts insie the data proerty but should not create problems in those cases.

Fixes #58

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.06%. Comparing base (df2bc6d) to head (27e6c79).
Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #59      +/-   ##
==========================================
+ Coverage   88.88%   90.06%   +1.17%     
==========================================
  Files          12       12              
  Lines         297      302       +5     
==========================================
+ Hits          264      272       +8     
+ Misses         33       30       -3     

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