Use random module to produce an actually unique file name

[Lukas0907]

During tests I noticed that flask_mailman would not produce one log file per message but actually sometimes append a message to an existing mail log file. By looking at the code I noticed that the file name of the log is derived from the ID of the object which might be reused (see also https://stackoverflow.com/q/20753364/172822 for a discussion). To get a truly unique file name I changed the code so that randrange() is used.

[marktennyson]

It's an valueable observation and fix. But one thing I wondered to know, why you using random.randint ? Instead of this you can use the current timestamp using time.time().

[Lukas0907]

But one thing I wondered to know, why you using random.randint ? Instead of this you can use the current timestamp using time.time().

What advantage would that have? The idea of the fix is that it's basically impossible to have two log files with the same name. That's not guaranteed with time.time().

[codecov]

Codecov Report

Merging #30 (bce9272) into master (6558b3a) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #30      +/-   ##
==========================================
+ Coverage   63.03%   63.10%   +0.06%     
==========================================
  Files           9        9              
  Lines         579      580       +1     
==========================================
+ Hits          365      366       +1     
  Misses        214      214              

Impacted Files	Coverage Δ
flask_mailman/backends/file.py	86.04% <100.00%> (+0.33%)	⬆️

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