FEC-320 - "undefined" is shown when the caption has no text in it

@itaykinnrot it's not an undefined variable. In this case, captionObj.content = "undefined", because the convertTTML2HTML function has the "return" statement within the "if( node.childNodes.length )", which is 0 when there's no text.
Maybe it would be better to handle it within the convertTTML2HTML function (just add an "else" statement which returns an empty string).