fix from_data_frame factory method with prediction df

[daMichaelB]

What does this PR do?

closes #1086

Creating an ImageClassificationData object with the from_data_frame factory method, was only working as long as i do not set

• predict_images_root
• predict_data_frame

Fixes #1086

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see #1086

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all tests in test_data.py are working

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[codecov]

Codecov Report

Merging #1088 (0f7df42) into master (4d00c34) will increase coverage by 0.05%.
The diff coverage is 100.00%.

❗ Current head 0f7df42 differs from pull request most recent head b64b621. Consider uploading reports for the commit b64b621 to get more accurate results

@@            Coverage Diff             @@
##           master    #1088      +/-   ##
==========================================
+ Coverage   87.75%   87.80%   +0.05%     
==========================================
  Files         281      281              
  Lines       12793    12793              
==========================================
+ Hits        11226    11233       +7     
+ Misses       1567     1560       -7     

Flag	Coverage Δ
unittests	87.80% <100.00%> (+0.05%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
flash/image/classification/data.py	97.50% <100.00%> (+5.00%)	⬆️
flash/image/classification/input.py	98.71% <0.00%> (+1.28%)	⬆️

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[ethanwharris]

Awesome! LGTM 😃