check response status in WSGIContext._app_call
check response status in WSGIContext._app_call

Only re-chain response iter if start_response hasn't been called yet.

Change-Id: I9670f49419104fb8f949e6edc12d9047d1289cde

bkolli/swift,maginatics/swift,hbhdytf/mac2,smerritt/swift,takeshineshiro/swift,redbo/swift,shibaniahegde/OpenStak_swift,Em-Pan/swift,IPVL/swift-kilo,Khushbu27/Tutorial,notmyname/swift,openstack/swift,psachin/swift,hbhdytf/mac,IPVL/swift-kilo,aerwin3/swift,psachin/swift,sarvesh-ranjan/swift,prashanthpai/swift,eatbyte/Swift,Triv90/SwiftUml,swiftstack/swift,tsli/test,bradleypj823/swift,matthewoliver/swift,smerritt/swift,hurricanerix/swift,Seagate/swift,bradleypj823/swift,xiaoguoai/ec-dev-swift,wenhuizhang/swift,scality/ScalitySproxydSwift,psachin/swift,wenhuizhang/swift,thiagodasilva/swift,Mirantis/swift-encrypt,zaitcev/swift-lfs,dpgoetz/swift,bkolli/swift,thiagodasilva/swift,dpgoetz/swift,Akanoa/swift,smerritt/swift,openstack/swift,swiftstack/swift,notmyname/swift,daasbank/swift,maginatics/swift,nadeemsyed/swift,aerwin3/swift,nadeemsyed/swift,psachin/swift,openstack/swift,clayg/swift,clayg/swift,mjwtom/swift,matthewoliver/swift,williamthegrey/swift,revoer/keystone-8.0.0,tipabu/swift,mjzmjz/swift,smerritt/swift,mjwtom/swift,hurricanerix/swift,tipabu/swift,AfonsoFGarcia/swift,swiftstack/swift,williamthegrey/swift,Triv90/SwiftUml,tipabu/swift,redhat-openstack/swift,AfonsoFGarcia/swift,hurricanerix/swift,orion/swift-config,larsbutler/swift,openstack/swift,revoer/keystone-8.0.0,hbhdytf/mac2,gold3bear/swift,redhat-openstack/swift,Khushbu27/Tutorial,redbo/swift,xiaoguoai/ec-dev-swift,clayg/swift,rackerlabs/swift,matthewoliver/swift,takeshineshiro/swift,mjzmjz/swift,notmyname/swift,levythu/swift,zaitcev/swift-lfs,hbhdytf/mac2,larsbutler/swift,NeCTAR-RC/swift,Seagate/swift,bouncestorage/swift,zackmdavis/swift,citrix-openstack/build-swift,orion/swift-config,notmyname/swift,levythu/swift,tipabu/swift,anishnarang/gswift,matthewoliver/swift,anishnarang/gswift,NeCTAR-RC/swift,nadeemsyed/swift,Mirantis/swift-encrypt,hbhdytf/mac,iostackproject/IO-Bandwidth-Differentiation,gold3bear/swift,sarvesh-ranjan/swift,hurricanerix/swift,clayg/swift,prashanthpai/swift,JioCloud/swift,citrix-openstack-build/swift,nadeemsyed/swift,citrix-openstack-build/swift,eatbyte/Swift,dencaval/swift,Akanoa/swift,dencaval/swift,rackerlabs/swift,tsli/test,Em-Pan/swift,citrix-openstack/build-swift,scality/ScalitySproxydSwift,shibaniahegde/OpenStak_swift,iostackproject/IO-Bandwidth-Differentiation,zackmdavis/swift,hbhdytf/mac2,daasbank/swift,JioCloud/swift,bouncestorage/swift