Fix zero byte files

[samschott]

Fixes an issue where data transport errors that are retried could result in zero byte files being created in the cloud if the local file size is smaller than 4 MB. This is caused by not rewinding to the beginning of the file before retrying the upload.

Note that chunked uploads for files > 4 MB are already handled correctly.

Fixes #925 and #926.

[codecov[bot]]

Codecov Report

Merging #945 (8683f08) into main (ce1b4b4) will increase coverage by 19.56%. The diff coverage is 100.00%.

@@             Coverage Diff             @@
##             main     #945       +/-   ##
===========================================
+ Coverage   59.01%   78.57%   +19.56%     
===========================================
  Files          42       42               
  Lines        7502     7506        +4     
===========================================
+ Hits         4427     5898     +1471     
+ Misses       3075     1608     -1467     

Flag	Coverage Δ
pytest	78.57% <100.00%> (+19.56%)	:arrow_up:

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Impacted Files	Coverage Δ
src/maestral/client.py	84.00% <100.00%> (+6.90%)	:arrow_up:

... and 15 files with indirect coverage changes

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[JNGRichardson]

Hope it's OK to comment here too (I'm new to GitHub, so not sure about etiquette). I'm not sure this issue has been fully fixed — I've been experiencing #925 in the latest versions, and several times since this fix. I've posted logs in my comment here: https://github.com/samschott/maestral/issues/925#issuecomment-2271967043