Fix cowboy_http_req:body with regard to the new accessors default value
Fix cowboy_http_req:body with regard to the new accessors default value

header/2 now returns 'undefined' when the header isn't in the request.

276361270/cowboy,CrankWheel/cowboy,essen/cowboy,ninenines/cowboy,layerhq/cowboy,grahamrhay/cowboy,acrispin/cowboy,pap/cowboy,omusico/cowboy,yangchengjian/cowboy,cad627/cowboy,piboye/cowboy,binarin/cowboy,LineMetrics/cowboy,chef/cowboy,imdeps/cowboy,bsmr-erlang/cowboy,unisontech/cowboy,LineMetrics/cowboy,cad627/cowboy,manastech/cowboy,linearregression/cowboyku,bobos/ecweb,piboye/cowboy,binarin/cowboy,K2InformaticsGmbH/cowboy,venkateshreddy/cowboy,LineMetrics/cowboy,rabbitmq/cowboy,layerhq/cowboy,noname007/cowboy,heroku/cowboy,lpgauth/cowboy,Reimerei/cowboy,callsign-core/cowboy_hybi00,ferd/cowboyku,callsign-core/cowboy_hybi00,unisontech/cowboy,yangchengjian/cowboy,turtleDeng/cowboy,odo/cowboy,MSch/cowboy,lpgauth/cowboy,heroku/cowboy,sile/cowboy,heroku/cowboyku,paulperegud/cowboy,dangjun625/cowboy,nviennot/cowboy,manastech/cowboy,essen/cowboy,rbalint/pkg-erlang-cowboy,kivra/cowboy,hairyhum/cowboy