Guard against null getResponseHeader('content-type') in clientSync
Guard against null getResponseHeader('content-type') in clientSync

From browser restrictions, jquery throwing a parseerror from malformed JSON, etc.
alexindigo/rendr,modulexcite/rendr,sarchila/rendr,rendrjs/rendr,SNASW/rendr,is00hcw/rendr,yhagio/rendr,eGood/rendr0.5,kball/rendr,0111001101111010/rendr,bigethan/rendr,CristinaFoltea/rendr