Added safeguard for PerformXPathQuery()
Added safeguard for PerformXPathQuery()

Making sure that app won't crash if nil is passed for query parameter.
CNMrGoat/hpple,Diveinedu-CN/hpple,TornadoBack/hpple,TornadoBack/hpple,0x1eaf/hpple,shanlilaide/hpple,topfunky/hpple,Diveinedu-CN/hpple,0x1eaf/hpple,qskycolor/hpple,tgcasce/hpple,qskycolor/hpple,WeiZhouhui/hpple,shanlilaide/hpple,WeiZhouhui/hpple,topfunky/hpple,tgcasce/hpple,CNMrGoat/hpple