Fix NPE crash in "slurp" middleware

[tatut]

Fallback to "application/octet-stream" if a content-type cannot be determined for the file/url.

Don't show the content of unrecognized files, but return a description "#binary[location=,size=".

Added test in slurp_test.clj to test unrecognized file.

[codecov]

Codecov Report

Merging #587 into master will decrease coverage by 0.04%.
The diff coverage is 78.57%.

@@            Coverage Diff             @@
##           master     #587      +/-   ##
==========================================
- Coverage   76.72%   76.68%   -0.05%     
==========================================
  Files          38       38              
  Lines        2389     2393       +4     
  Branches      138      140       +2     
==========================================
+ Hits         1833     1835       +2     
  Misses        418      418              
- Partials      138      140       +2

Impacted Files	Coverage Δ
src/cider/nrepl/middleware/content_type.clj	33.33% <0%> (ø)	⬆️
src/cider/nrepl/middleware/slurp.clj	60.52% <84.61%> (-0.59%)	⬇️

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[cichli]

Thanks for the contribution! Please will you rebase to master? It's just a small conflict. Note that this also conflicts with #589.

The changes look fine to me – @arrdem do you mind double-checking?

[arrdem]

LGTM, I'd like to see this all get better factored so that users can opt into different sets of binary file handling behavior. Not sure this is a good universal fallback, but I do believe it's better.

Thanks for the patch!

[cichli]

Cheers @tatut @arrdem!