Handle error responses that do not contain JSON

[micthiesen]

Closes #163

[codecov[bot]]

Codecov Report

Merging #164 into master will decrease coverage by 0.22%. The diff coverage is 60%.

@@            Coverage Diff             @@
##           master     #164      +/-   ##
==========================================
- Coverage     100%   99.77%   -0.23%     
==========================================
  Files          22       22              
  Lines         873      876       +3     
  Branches       74       74              
==========================================
+ Hits          873      874       +1     
- Misses          0        2       +2

Impacted Files	Coverage Δ
postmarker/core.py	97.8% <60%> (-2.2%)	:arrow_down:

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[Stranger6667]

Hej! Thank you for your contribution! :)

Could you give me some example of such payload from Postmark?

[micthiesen]

Hey np! I wasn't able to retrieve an example payload yet since the ValueError that was being raised didn't include much useful information.

Since our use case with Postmark is very simple, we're going to switch to use requests in our app. If it happens again I'll update this PR with what the response looks like. In the meantime feel free to close this.

[Stranger6667]

I believe, that the case is important indeed and I'm happy to merge it :) I'll take care about the testing later

[Stranger6667]

Released in 0.12.1

[micthiesen]

Thanks for the quick release! Much appreciated.

[Stranger6667]

You're welcome :)