net/rpc: don't assume b.N > 0
net/rpc: don't assume b.N > 0

Change-Id: I58c4a75168fd1f797a25735c4151f501f0475332
Reviewed-on: https://go-review.googlesource.com/20854
Reviewed-by: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

golang/go,vanloswang/go,ganboing/go-esx,nawawi/go,CAFxX/go,suncycheng/go,akutz/go,ImJasonH/go,miolini/go,momchil-velikov/go,suncycheng/go,ImJasonH/go,theif519/go,vanloswang/go,josharian/go,polyverse-security/go,CAFxX/go,golang/go,josharian/go,nawawi/go,christopher-henderson/Go,nawawi/go,4ad/go,golang/go,Cofyc/go,CAFxX/go,goodlang/good,miolini/go,akutz/go,codestation/go,derekmarcotte/go,theif519/go,linux-on-ibm-z/go,vsekhar/elastic-go,ImJasonH/go,Cofyc/go,cloudflare/go,linux-on-ibm-z/go,ImJasonH/go,derekmarcotte/go,ganboing/go-esx,derekmarcotte/go,golang/go,CAFxX/go,CAFxX/go,linux-on-ibm-z/go,cloudflare/go,goodlang/good,theif519/go,CAFxX/go,ImJasonH/go,4ad/go,cloudflare/go,golang/go,codestation/go,cloudflare/go,goodlang/good,vsekhar/elastic-go,vanloswang/go,codestation/go,momchil-velikov/go,vanloswang/go,goodlang/good,derekmarcotte/go,derekmarcotte/go,polyverse-security/go,ImJasonH/go,codestation/go,vsekhar/elastic-go,vanloswang/go,vanloswang/go,CAFxX/go,momchil-velikov/go,goodlang/good,ganboing/go-esx,4ad/go,4ad/go,4ad/go,theif519/go,theif519/go,derekmarcotte/go,josharian/go,nawawi/go,theif519/go,cloudflare/go,josharian/go,linux-on-ibm-z/go,akutz/go,miolini/go,nawawi/go,momchil-velikov/go,nawawi/go,theif519/go,vsekhar/elastic-go,vsekhar/elastic-go,Cofyc/go,akutz/go,cloudflare/go,nawawi/go,suncycheng/go,4ad/go,Cofyc/go,josharian/go,goodlang/good,suncycheng/go,josharian/go,theif519/go,codestation/go,ganboing/go-esx,momchil-velikov/go,akutz/go,goodlang/good,polyverse-security/go,akutz/go,linux-on-ibm-z/go,miolini/go,suncycheng/go,golang/go,ganboing/go-esx,ganboing/go-esx,4ad/go,Cofyc/go,vsekhar/elastic-go,miolini/go,linux-on-ibm-z/go,polyverse-security/go,polyverse-security/go,codestation/go,suncycheng/go,codestation/go,momchil-velikov/go,CAFxX/go,Cofyc/go,polyverse-security/go,miolini/go,vsekhar/elastic-go,josharian/go,momchil-velikov/go,linux-on-ibm-z/go,linux-on-ibm-z/go,suncycheng/go,golang/go,codestation/go,ganboing/go-esx,momchil-velikov/go,derekmarcotte/go,cloudflare/go,josharian/go,golang/go,polyverse-security/go,vsekhar/elastic-go,vanloswang/go,Cofyc/go,ganboing/go-esx,suncycheng/go,derekmarcotte/go,polyverse-security/go,miolini/go,vanloswang/go,cloudflare/go,akutz/go,miolini/go,Cofyc/go,goodlang/good,4ad/go,ImJasonH/go,akutz/go,nawawi/go,ImJasonH/go