Only do the hasAttribute check if the method exists - IE falls back t…

…o the === null check below which allows this to still work. Follow-up to cb40495 - thanks to @jitter for the catch.

src/attributes.js

@@ -332,7 +332,7 @@ jQuery.extend({
 
 			// Ensure that missing attributes return undefined
 			// Blackberry 4.7 returns "" from getAttribute #6938
-			if ( !elem.attributes[ name ] && !elem.hasAttribute( name ) ) {
+			if ( !elem.attributes[ name ] && (elem.hasAttribute && !elem.hasAttribute( name )) ) {
 				return undefined;
 			}