[jdom-interest] Tiny optimization

[Laurent Bihanic]

In SAXHandler, in method characters() changing
         if (suppress) return;
into
         if ((suppress) || (length == 0)) return;
reduces by 5% the parsing time when using Crimson. Apparently this latter 
reports line breaks as character data of length 0.

The same should apply to ignorableWhitespace().

Laurent