Raise 400 error in case of content_type json but empty body

[inkhey]

Currently:

origin : https://github.com/algoo/hapic/issues/184 We accept empty body of content_type json request in pyramid context (and maybe other context)

Expected:

• Raise 400 error in case of unvalid json for content_type json request, including empty body, on all context (to have similar behavior)
• Tracim should work with https://github.com/tracim/tracim/issues/1871 fix.