Fix #86 -- Catch and log file not found exception

[codingjoe]

No description provided.

[codecov]

Codecov Report

Merging #91 into master will decrease coverage by 1.33%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##           master      #91      +/-   ##
==========================================
- Coverage     100%   98.66%   -1.34%     
==========================================
  Files           4        4              
  Lines          69       75       +6     
==========================================
+ Hits           69       74       +5     
- Misses          0        1       +1

Impacted Files	Coverage Δ
s3file/middleware.py	95.45% <85.71%> (-4.55%)	⬇️

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