Merge pull request #90 from jwestbrook/IE8Opacityfix

Prevent exception in IE when calling `Element.getOpacity`.

Author: savetheclocktower

src/prototype/dom/dom.js

@@ -3000,7 +3000,7 @@
     var filter = Element.getStyle(element, 'filter');
     if (filter.length === 0) return 1.0;
     var match = (filter || '').match(/alpha\(opacity=(.*)\)/);
-    if (match[1]) return parseFloat(match[1]) / 100;
+    if (match && match[1]) return parseFloat(match[1]) / 100;
     return 1.0;
   }
 
@@ -3478,4 +3478,4 @@
   if (window.attachEvent)
     window.attachEvent('onunload', destroyCache_IE);
 
-})(this);
+})(this);