More robust array type check. p=mwootendev, r=me (closes #2959)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@12095 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Format/WMC/v1.js

@@ -1154,7 +1154,7 @@ OpenLayers.Format.WMC.v1 = OpenLayers.Class(OpenLayers.Format.XML, {
         var node = this.createElementDefaultNS("StyleList");
 
         var styles = layer.styles;
-        if (styles && styles instanceof Array) {
+        if (styles && OpenLayers.Util.isArray(styles)) {
             var sld;
             for (var i=0, len=styles.length; i<len; i++) {
                 var s = styles[i];