fix index out of range panic in reference link
fix index out of range panic in reference link

Add checking before accessing the input data.

Fix #172 and #173 issues.

Signed-off-by: Tw <9badae619f85d6141021d55221ac5bc6f13849e6@gmail.com>

beni55/blackfriday,Go-ApiBlueprint-Go/blackfriday,tianon/debian-golang-blackfriday,jmptrader/blackfriday,jacobxk/blackfriday,linuxerwang/blackfriday,ArtemTeleshev/blackfriday,Depado/blackfriday,Ganners/blackfriday,JackKnifed/blackfriday,apiaryio/blackfriday,linuxerwang/blackfriday,Ganners/blackfriday,kristofer/blackfriday,elian0211/blackfriday,DimShadoWWW/blackfriday,ckeyer/blackfriday,kristofer/blackfriday,elian0211/blackfriday,icco/blackfriday,tianon/debian-golang-blackfriday,Ronmi/blackfriday,Go-ApiBlueprint-Go/blackfriday,icco/blackfriday,beni55/blackfriday,Ronmi/blackfriday,jacobxk/blackfriday,Depado/blackfriday,ckeyer/blackfriday,treejames/blackfriday,lfn3/blackfriday,jmptrader/blackfriday,treejames/blackfriday,apiaryio/blackfriday,lfn3/blackfriday,JackKnifed/blackfriday,DimShadoWWW/blackfriday,ArtemTeleshev/blackfriday