don't allow a baselayer to unselect itself

git-svn-id: http://svn.openlayers.org/trunk/openlayers@1134 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Control/LayerSwitcher.js

@@ -121,9 +121,11 @@ OpenLayers.Control.LayerSwitcher.prototype =
             var labelSpan = document.createElement("span");
             labelSpan.innerHTML = layer.name;
             labelSpan.style.verticalAlign = (baseLayer) ? "bottom" : "auto";
-            Event.observe(labelSpan, 
-                          "click", 
-                          this.onLabelClick.bindAsEventListener(inputElem));
+            if (!(baseLayer && checked)) {
+                Event.observe(labelSpan, 
+                              "click", 
+                             this.onLabelClick.bindAsEventListener(inputElem));
+            }
 
             // create line break
             var br = document.createElement("br");