Only show 'switch to layer' button if layer not already selected.

src/components/App.jsx

@@ -732,6 +732,7 @@ export default class App extends React.Component {
     /> : null
 
     const bottomPanel = (this.state.errors.length + this.state.infos.length) > 0 ? <MessagePanel
+      currentLayer={selectedLayer}
       onLayerSelect={this.onLayerSelect}
       mapStyle={this.state.mapStyle}
       errors={this.state.errors}

src/components/MessagePanel.jsx

@@ -7,6 +7,7 @@ class MessagePanel extends React.Component {
     infos: PropTypes.array,
     mapStyle: PropTypes.object,
     onLayerSelect: PropTypes.func,
+    currentLayer: PropTypes.object,
   }
 
   static defaultProps = {
@@ -18,11 +19,14 @@ class MessagePanel extends React.Component {
       let content;
       if (error.parsed && error.parsed.type === "layer") {
         const {parsed} = error;
-        const {mapStyle} = this.props;
+        const {mapStyle, currentLayer} = this.props;
         const layerId = mapStyle.layers[parsed.data.index].id;
         content = (
           <>
-            Layer <span>&apos;{layerId}&apos;</span>: {parsed.data.message} &mdash;&nbsp;
+            Layer <span>&apos;{layerId}&apos;</span>: {parsed.data.message}
+            {currentLayer.id !== layerId &&
+              <>
+                &nbsp;&mdash;&nbsp;
                 <button
                   className="maputnik-message-panel__switch-button"
                   onClick={() => this.props.onLayerSelect(layerId)}
@@ -30,6 +34,8 @@ class MessagePanel extends React.Component {
                   switch to layer
                 </button>
               </>
+            }
+          </>
         );
       }
       else {