check Content-Type

[eivindfjeldstad]

we should throw if Content-Type is something other than multipart/form-data

[fengmk2]

pr welcome

[hodonsky]

Please add suggestion to error thrown related to this. I was unsure of requirement that it would fail and not continue or return an empty object, it would be nice if this was flagged on the returned object instead of just failing. eg: parts.multipart === false // true; or maybe parts.length would return 0, empty array?