same-case these functions for if there is no baselayer. in theory,

these should never be called if no baselayer is set... but one never
knows what a user will do. So instead of crashing, we will just return null.


git-svn-id: http://svn.openlayers.org/trunk/openlayers@857 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Map.js

@@ -641,27 +641,47 @@ OpenLayers.Map.prototype = {
 
     /**
      * @returns A Bounds object which represents the lon/lat bounds of the 
-     *          current viewPort.
+     *          current viewPort. 
+     *          If no baselayer is set, returns null.
      * @type OpenLayers.Bounds
      */
     getExtent: function () {
-        return this.baseLayer.getExtent();
+        var extent = null;
+        
+        if (this.baseLayer != null) {
+            extent = this.baseLayer.getExtent();
+        }
+        return extent;
     },
 
     /**
-    * @type float
+     * @returns The current resolution of the map. 
-    */
+     *          If no baselayer is set, returns null.
+     * @type float
+     */
     getResolution: function () {
-        return this.baseLayer.getResolution();
+        var resolution = null;
+        
+        if (this.baseLayer != null) {
+            resolution = this.baseLayer.getResolution();
+        }
+        return resolution;
     },
 
     /**
     * @param {OpenLayers.Bounds} bounds
     *
+    * @returns A suitable zoom level for the specified bounds.
+    *          If no baselayer is set, returns null.
     * @type int
     */
     getZoomForExtent: function (bounds) {
-        return this.baseLayer.getZoomForExtent(bounds);        
+        zoom = null;
+        
+        if (this.baseLayer != null) {
+            zoom = this.baseLayer.getZoomForExtent(bounds);
+        }
+        return zoom;
     },
 
   /********************************************************/