a grid layer may be moved while its grid hasn't been initialized yet, r=ahocevar (references #3458)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@12236 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Map.js

@@ -1722,7 +1722,8 @@ OpenLayers.Map = OpenLayers.Class({
             var layer, i, len;
             for (i=0, len=this.layers.length; i<len; ++i) {
                 layer = this.layers[i];
-                if (layer.visibility) {
+                if (layer.visibility &&
+                    (layer === this.baseLayer || layer.inRange)) {
                     layer.moveByPx(dx, dy);
                     layer.events.triggerEvent("move");
                 }