Bump milsymbol version, test for layer control before removal

package.json

@@ -1,6 +1,6 @@
 {
     "name": "node-red-contrib-web-worldmap",
-    "version": "2.0.12",
+    "version": "2.0.13",
     "description": "A Node-RED node to provide a web page of a world map for plotting things on.",
     "dependencies": {
         "cgi": "0.3.1",

worldmap/worldmap.js

@@ -1501,7 +1501,7 @@ function doCommand(cmd) {
     if (cmd.hasOwnProperty("showlayers")) {
         if ((cmd.showlayers === "hide") && (showLayerMenu === true)) {
             showLayerMenu = false;
-            layercontrol.removeFrom(map);
+            if (layercontrol) { layercontrol.removeFrom(map); }
         }
         else if ((cmd.showlayers === "show") && (showLayerMenu === false)) {
             showLayerMenu = true;