do not catch ValueError exceptions inside method by mistake

I had an encoding issue with data passed to worksheet.write, that made the python codecs module to raise a  UnicodeDecodeError exception.

UnicodeDecodeError is a ValueError descendant (http://docs.python.org/2/library/exceptions.html#exception-hierarchy), so the code took an unwanted path. 

My approach here is to leave only the possibly failing int(args[0]) line in the try block, moving the method call outside of the try.