Allow link jumps to tags without text in cr3.

Some books specify empty tags as TOC link targets, like:
<a id="someId"> </a>. CR3 is jumping to page 0 instead.

The problem is that ldomXPointer::getRect returns false when there is not text and rect is empty. I've modified that behavior and when explicitly set (call parameter linkTarget set to true) it returns true and top left corrdinates of the rect returned are set correctly. Those two corrdinates are used only when a link target page is determined and that is the only scenario when getRect is called with linkTarget parameter set to true (TOC jump, link on page jump).