fs: validate falsy openAsBlob type option

[christianaurichzm]

openAsBlob() and openAsBlobSync() use options.type || '' before validating the option. This causes falsy non-string values such as null, false, 0, and NaN to be silently replaced with the default empty string instead of throwing ERR_INVALID_ARG_TYPE.

This changes the defaulting behavior so only undefined uses the empty string default. All other values are passed to validateString().

Tests were added for the affected falsy non-string values.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.29%. Comparing base (b125121) to head (0545339).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66125      +/-   ##
==========================================
- Coverage   90.29%   90.29%   -0.01%     
==========================================
  Files         790      790              
  Lines      271689   271784      +95     
  Branches    51856    51877      +21     
==========================================
+ Hits       245312   245395      +83     
- Misses      16878    16888      +10     
- Partials     9499     9501       +2     

Files with missing lines	Coverage Δ
lib/fs.js	97.32% <100.00%> (ø)

... and 27 files with indirect coverage changes

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