BUG: map_chunk wrong results when input is empty data

[ChengjieLi28]

What do these changes do?

Related issue number

Fixes #723

Check code requirements

• tests added / passed (if needed)
• Ensure all linting tests pass

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 49.64%. Comparing base (b320ca3) to head (9cb4f26).
⚠️ Report is 63 commits behind head on main.

Files with missing lines	Patch %	Lines
python/xorbits/_mars/dataframe/base/map_chunk.py	0.00%	3 Missing ⚠️

❌ Your project check has failed because the head coverage (49.64%) is below the target coverage (90.00%). You can increase the head coverage or adjust the target coverage.

❗ There is a different number of reports uploaded between BASE (b320ca3) and HEAD (9cb4f26). Click for more details.

HEAD has 20 uploads less than BASE

Flag	BASE (b320ca3)	HEAD (9cb4f26)
unittests	22	2

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #727       +/-   ##
===========================================
- Coverage   82.55%   49.64%   -32.91%     
===========================================
  Files        1058     1058               
  Lines       79780    79775        -5     
  Branches    16504    12431     -4073     
===========================================
- Hits        65861    39604    -26257     
- Misses      11645    38581    +26936     
+ Partials     2274     1590      -684     

Flag	Coverage Δ
unittests	49.63% <0.00%> (-32.79%)	⬇️

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