cubicweb #4421845 [wsgi] Posting non-forms data fails [done]

Because any posted content is processed by multipart.py, posting non-form data raise errors.

prioritynormal
typebug
done in<not specified>
load left0.000
closed by#c9f1111e0ee8 [wsgi] If multipart cannot parse the POST content, let it pass.
patch[wsgi] If multipart cannot parse the POST content, let it pass. [applied]