net: check 'ok' return in dnsmsg when initially packing rr.Header()
net: check 'ok' return in dnsmsg when initially packing rr.Header()

In the present code, there is no way for ok to ever return false, but
it still a good idea to check it.

Change-Id: I8f360018b33a5d85dabbbbec0f89ffc81f77ecbb
Reviewed-on: https://go-review.googlesource.com/13956
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

4ad/go,codestation/go,rachtsingh/gogojuice,deft-code/go,suncycheng/go,binarycrusader/go,theif519/go,ganboing/go-esx,Pulgafree/go,rachtsingh/gogojuice,CAFxX/go,golang/go,sndnvaps/go,jacobhaven/go,cloudflare/go,binarycrusader/go,4ad/go,NunoEdgarGub1/go,Pulgafree/go,Pulgafree/go,polyverse-security/go,joshsammut/go,likesea/go,theif519/go,malvira/go,linux-on-ibm-z/go,theif519/go,ichu501/go,Cofyc/go,CarterTsai/go,mikekap/go,Endika/go,CAFxX/go,jonasi/go,yasarkunduz/go,beealone/go,josharian/go,rachtsingh/gogojuice,cyberroadie/go,sndnvaps/go,deft-code/go,golang/go,Cofyc/go,kim-racktop/go,ichu501/go,samanalysis/go,NunoEdgarGub1/go,josharian/go,Jordanzuo/go,xiuzhifu/go,cloudflare/go,samanalysis/go,linux-on-ibm-z/go,xiuzhifu/go,4ad/go,odeke-em/go,gdey/go,codestation/go,binarycrusader/go,binarycrusader/go,cloudflare/go,kim-racktop/go,fjballest/golang,yasarkunduz/go,ImJasonH/go,cloudflare/go,akutz/go,Cofyc/go,CAFxX/go,CAFxX/go,polyverse-security/go,cookerzhu/go,roth1002/go,dterei/go,jdhenke/go,roth1002/go,vsekhar/elastic-go,snowsnail/go,cyberroadie/go,miolini/go,4ad/go,gdey/go,vanloswang/go,jonasi/go,b54898533/go,likesea/go,akutz/go,dterei/go,Samurais/go,roth1002/go,jacobhaven/go,nawawi/go,samanalysis/go,theif519/go,GeorgiCodes/go,fjballest/golang,4ad/go,beealone/go,gdey/go,vanloswang/go,golang/go,sndnvaps/go,goodlang/good,cloudflare/go,ImJasonH/go,gdey/go,Cofyc/go,GeorgiCodes/go,nawawi/go,malvira/go,goodlang/good,polyverse-security/go,xiuzhifu/go,Endika/go,codestation/go,theif519/go,likesea/go,jacobsa/go,alex-zhang/go,kim-racktop/go,Cofyc/go,GeorgiCodes/go,derekmarcotte/go,ImJasonH/go,CarterTsai/go,cyberroadie/go,cyberroadie/go,cookerzhu/go,xiuzhifu/go,cookerzhu/go,yasarkunduz/go,likesea/go,beealone/go,codestation/go,theif519/go,suncycheng/go,NunoEdgarGub1/go,Samurais/go,vsekhar/elastic-go,jdhenke/go,joshsammut/go,Endika/go,vsekhar/elastic-go,cyberroadie/go,kim-racktop/go,mikekap/go,linux-on-ibm-z/go,alex-zhang/go,jacobhaven/go,nawawi/go,linux-on-ibm-z/go,jdhenke/go,gdey/go,vsekhar/elastic-go,roth1002/go,ichu501/go,Jordanzuo/go,derekmarcotte/go,nawawi/go,ImJasonH/go,b54898533/go,jdhenke/go,derekmarcotte/go,vanloswang/go,jonasi/go,fjballest/golang,rachtsingh/gogojuice,dterei/go,ImJasonH/go,josharian/go,Pulgafree/go,vanloswang/go,cookerzhu/go,NunoEdgarGub1/go,vanloswang/go,GeorgiCodes/go,kim-racktop/go,snowsnail/go,beealone/go,derekmarcotte/go,theif519/go,Pulgafree/go,goodlang/good,Pulgafree/go,4ad/go,christopher-henderson/Go,jacobhaven/go,NunoEdgarGub1/go,joshsammut/go,cloudflare/go,binarycrusader/go,rachtsingh/gogojuice,akutz/go,akutz/go,CarterTsai/go,beealone/go,nawawi/go,Samurais/go,b54898533/go,ichu501/go,mwhudson/go,jacobsa/go,malvira/go,CarterTsai/go,golang/go,ganboing/go-esx,jacobhaven/go,dterei/go,nawawi/go,Endika/go,alex-zhang/go,alex-zhang/go,miolini/go,alex-zhang/go,roth1002/go,CarterTsai/go,sndnvaps/go,rachtsingh/gogojuice,yasarkunduz/go,sndnvaps/go,fjballest/golang,jacobhaven/go,momchil-velikov/go,b54898533/go,odeke-em/go,snowsnail/go,theif519/go,dterei/go,polyverse-security/go,jdhenke/go,vsekhar/elastic-go,kim-racktop/go,odeke-em/go,4ad/go,dterei/go,vanloswang/go,GeorgiCodes/go,malvira/go,gdey/go,fjballest/golang,linux-on-ibm-z/go,joshsammut/go,deft-code/go,deft-code/go,Samurais/go,b54898533/go,jonasi/go,ichu501/go,likesea/go,goodlang/good,xiuzhifu/go,odeke-em/go,mikekap/go,vsekhar/elastic-go,jdhenke/go,momchil-velikov/go,rachtsingh/gogojuice,deft-code/go,odeke-em/go,4ad/go,ganboing/go-esx,miolini/go,momchil-velikov/go,Cofyc/go,GeorgiCodes/go,odeke-em/go,momchil-velikov/go,goodlang/good,kim-racktop/go,b54898533/go,golang/go,codestation/go,ganboing/go-esx,samanalysis/go,GeorgiCodes/go,jacobsa/go,fjballest/golang,momchil-velikov/go,beealone/go,yasarkunduz/go,mwhudson/go,suncycheng/go,cyberroadie/go,derekmarcotte/go,ganboing/go-esx,jacobsa/go,snowsnail/go,derekmarcotte/go,snowsnail/go,codestation/go,momchil-velikov/go,Endika/go,ichu501/go,likesea/go,akutz/go,suncycheng/go,ganboing/go-esx,ichu501/go,miolini/go,ImJasonH/go,suncycheng/go,roth1002/go,linux-on-ibm-z/go,akutz/go,Pulgafree/go,CAFxX/go,linux-on-ibm-z/go,cloudflare/go,vanloswang/go,NunoEdgarGub1/go,golang/go,deft-code/go,gdey/go,nawawi/go,linux-on-ibm-z/go,Endika/go,sndnvaps/go,jonasi/go,josharian/go,mwhudson/go,polyverse-security/go,joshsammut/go,NunoEdgarGub1/go,Jordanzuo/go,miolini/go,vsekhar/elastic-go,alex-zhang/go,beealone/go,alex-zhang/go,likesea/go,mwhudson/go,Jordanzuo/go,Endika/go,mikekap/go,xiuzhifu/go,jonasi/go,malvira/go,jdhenke/go,golang/go,josharian/go,joshsammut/go,snowsnail/go,codestation/go,Jordanzuo/go,b54898533/go,yasarkunduz/go,CarterTsai/go,momchil-velikov/go,rachtsingh/gogojuice,Jordanzuo/go,sndnvaps/go,Samurais/go,CarterTsai/go,Pulgafree/go,xiuzhifu/go,derekmarcotte/go,cyberroadie/go,ganboing/go-esx,jacobhaven/go,Samurais/go,cookerzhu/go,miolini/go,yasarkunduz/go,kim-racktop/go,b54898533/go,derekmarcotte/go,binarycrusader/go,ImJasonH/go,jacobsa/go,binarycrusader/go,GeorgiCodes/go,gdey/go,goodlang/good,cyberroadie/go,yasarkunduz/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