Do not split download if no "Content-length"

[rlaker]

The server I was downloading from does not return a "Content-length" in the response, leading to a KeyError and a failed download.

I did get it working when DISABLE_RANGE was set, but since this is an environment variable I cannot change this in the code, since other servers I download from do return "Content-length".

I have now added an extra statement to check if "Content-length" is in the response, otherwise do not try and split the download.

Let me know what you think.

[codecov]

Codecov Report

Merging #87 (30ebdf4) into main (9afc7cf) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #87   +/-   ##
=======================================
  Coverage   91.52%   91.52%           
=======================================
  Files           4        4           
  Lines         425      425           
=======================================
  Hits          389      389           
  Misses         36       36           

Impacted Files	Coverage Δ
parfive/downloader.py	94.85% <100.00%> (ø)

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[Cadair]

Looks good to me, thanks a lot for the PR :)

[Cadair]

I need to fix the CI and then I shall make a release 😄