Fix overlay code

so that overlays with no 'overlay' config are always displayed

overviewer_core/data/js_src/views.js

@@ -269,7 +269,10 @@ overviewer.views.OverlayControlView = Backbone.View.extend({
         
         for (i in mapTypes) {
             var mt = mapTypes[i];
-            if (mt.tiles.indexOf(currentTileSetPath)!=-1) {
+            // if this overlay specifies a list of valid tilesets, then skip over any invalid tilesets 
+            if ((mt.tiles.length > 0) && (mt.tiles.indexOf(currentTileSetPath) ==-1)) {
+                continue;
+            }
             this.addItem({label: mt.name,
                     name: mt.name,
                     mt: mt,
@@ -290,8 +293,7 @@ overviewer.views.OverlayControlView = Backbone.View.extend({
                         }
 
                     }
-                        })
-            }
+            });
         }