It would be a good and small enhancement to have a javascript client-side check
for the RemoveLayer and LayerOrder widget on whether or not a layer has been
selected. This will save the user some submits ...

Something like

     if ({$this->mszHTMLForm}.SELECTED_LAYERS == null ||
         {$this->mszHTMLForm}.SELECTED_LAYERS.value == null ||
         {$this->mszHTMLForm}.SELECTED_LAYERS.value == "" )
     {
         alert( "No layer selected." );
         return;
     }