Fix the error where GIF file thumbnails could not be created properly

[pk5ls20]

reference: https://github.com/python-pillow/Pillow/issues/4313

[codeclimate[bot]]

Code Climate has analyzed commit 9d678999 and detected 0 issues on this pull request.

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 79.48%. Comparing base (f6c9d85) to head (9d67899).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #37 +/- ## ======================================= Coverage 79.48% 79.48% ======================================= Files 29 29 Lines 1272 1272 ======================================= Hits 1011 1011 Misses 261 261 ```

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