Prevent calls to getLayoutProperty from causing fatal error when laye…

…r doesn't exist

src/style/style.js

@@ -786,12 +786,18 @@ class Style extends Evented {
 
     /**
      * Get a layout property's value from a given layer
-     * @param {string} layer the layer to inspect
+     * @param {string} layerId the layer to inspect
      * @param {string} name the name of the layout property
      * @returns {*} the property value
      */
-    getLayoutProperty(layer: string, name: string) {
-        return this.getLayer(layer).getLayoutProperty(name);
+    getLayoutProperty(layerId: string, name: string) {
+        const layer = this.getLayer(layerId);
+        if (!layer) {
+            this.fire(new ErrorEvent(new Error(`The layer '${layerId}' does not exist in the map's style.`)));
+            return;
+        }
+
+        return layer.getLayoutProperty(name);
     }
 
     setPaintProperty(layerId: string, name: string, value: any) {