Catch xml2js errors caused by sax

xml2js fails to call the callback function with  err set in case of parse errors, because sax.js throws a global error (Line 912 sax.js). 
This throwed error is never catched and therefore bumps at top level, so its not possible to do a needle call with automatic xml parsing. (One has to switch off parsing).

This patch catches the error and calls the callback in the intended way.