need to make sure a size has been declared before trying to set the offset. thank you automated testing for finding this one.

git-svn-id: http://svn.openlayers.org/trunk/openlayers@130 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Icon.js

@@ -27,7 +27,7 @@ OpenLayers.Icon.prototype = {
         this.url = url;
 
         this.offset = offset;
-        if (offset == null) {
+        if ((size != null) && (offset == null)) {
             // default offset
             this.offset = new OpenLayers.Pixel(-(size.w / 2), -size.h);
         }