fix DataFrame NaN values becoming 0 after sorting (#12890)
* fix dataframe NaN values becoming 0 after sorting
Number(null) returns 0 in JavaScript, so when null values (representing
NaN from pandas) pass through cast_value_to_type with datatype 'number',
they get converted to 0 instead of being preserved.
Added an early return for null/undefined values before any type coercion.
Closes #12544
Closes #12554
* add changeset
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Co-authored-by: Hannah <hannahblair@users.noreply.github.com>
Co-authored-by: gradio-pr-bot <gradio-pr-bot@users.noreply.github.com>
