Ensure that pie's legendWidth remains numeric.

Substitute zero when .width() returns undefined, since legendWidth is
used in numeric calculations that break when it is undefined.  This
became a problem with the release of jQuery 1.8.0, which returns
undefined instead of null when an element doesn't exist.  This was fixed
in 1.8.1, but this is good practice anyway.

jquery.flot.pie.js

@@ -191,7 +191,7 @@ More detail and specific examples can be found in the included HTML file.
 		
 		function setupPie()
 		{
-			legendWidth = target.children().filter('.legend').children().width();
+			legendWidth = target.children().filter('.legend').children().width() || 0;
 		
 			// calculate maximum radius and center point
 			maxRadius =  Math.min(canvasWidth,(canvasHeight/options.series.pie.tilt))/2;