fix(API): Content-Length header not set for 416 status

The latest HTTP 1.1 RFC states that the Content-Length header MUST NOT be
set for 1xx and 204. It is also normally not set for 304. 416 is not
mentioned, so we should set Content-Length for it.
Merge pull request #283 from kgriffs/bug

fix(API): Content-Length header not set for 416 status