Potential fix for incorrect reading of data with empty cells when used with pyexcel

[mtskelton]

Ran into the same problem as reported on issue #8 today and implemented a workaround.
It's a somewhat rushed fix so may need some refactoring (which I will do if I have some further free time), but I'm opening the PR in case you find it useful.

[chfw]

thanks for your PR! could you please write unit tests for your code change?

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 92.30769% with 1 line in your changes missing coverage. Please review.

Project coverage is 97.37%. Comparing base (80bd1e4) to head (057cea8).
Report is 2 commits behind head on dev.

Files with missing lines	Patch %	Lines
pyexcel_xlsxr/messy_xlsx.py	92.30%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##              dev       #9      +/-   ##
==========================================
- Coverage   97.52%   97.37%   -0.15%     
==========================================
  Files          11       11              
  Lines         444      457      +13     
==========================================
+ Hits          433      445      +12     
- Misses         11       12       +1     

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[shrpow]

wtf its still not fixed