runtime: don't assume b.N > 0
runtime: don't assume b.N > 0

Change-Id: I2e26717f2563d7633ffd15f4adf63c3d0ee3403f
Reviewed-on: https://go-review.googlesource.com/20856
Run-TryBot: Marcel van Lohuizen <a22d082192f3ccf984644a4f482781f4c2d65180@golang.org>
Reviewed-by: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

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