[Patch] Fix crash when clicking on the foot note button (younes branch)

[Abdelrazak Younes]

As the former one, this one is obviously correct and I need it for my 
branch so I'll commit it now.

Abdel.
Index: text.C
===================================================================
--- text.C      (revision 14346)
+++ text.C      (working copy)
@@ -2245,6 +2245,9 @@
 {
        //lyxerr << "LyXText::cursorY: boundary: " << boundary << std::endl;
        Paragraph const & par = getPar(sl.pit());
+       if (par.rows().empty())
+               return 0;
+
        int h = 0;
        h -= pars_[0].rows()[0].ascent();
        for (pit_type pit = 0; pit < sl.pit(); ++pit)