Handle the format '?' in number formatting

[kurtinge]

Handle the format '?' in number formatting

Description

When excelize tries to read a cell where the formatCode in the style is "?" it will return an empty string instead of the number.

Motivation and Context

This handles that the formatCode "?" is valid and returns a the number correctly

How Has This Been Tested

This has been tested in the unit test and with an actual file.

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.20%. Comparing base (4324622) to head (4d7817c).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2080   +/-   ##
=======================================
  Coverage   99.20%   99.20%           
=======================================
  Files          32       32           
  Lines       30075    30075           
=======================================
  Hits        29837    29837           
  Misses        158      158           
  Partials       80       80           

Flag	Coverage Δ
unittests	99.20% <100.00%> (ø)

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[xuri]

Thanks for your PR. The case as I commented on above should be supported.