Fix for nan extents when using the 'zoom out' tool and height or width of window is 0

git-svn-id: http://svn.osgeo.org/qgis/trunk/qgis@6068 c8812cc2-4d05-0410-92ff-de0c093fc19c

Author: mhugent

src/gui/qgsmaptoolzoom.cpp

@@ -91,13 +91,20 @@ void QgsMapToolZoom::canvasReleaseEvent(QMouseEvent * e)
       double sf;
       if (mZoomRect.width() > mZoomRect.height())
       {
+	if(r.width() == 0)//prevent nan map extent
+	  {
+	    return;
+	  }
         sf = extent.width() / r.width();
       }
       else
       {
+	if(r.height() == 0)//prevent nan map extent
+	  {
+	    return;
+	  }
         sf = extent.height() / r.height();
       }
-              
       r.expand(sf);
 
   #ifdef QGISDEBUG