Work around IE issue.

This work around has the problem where the first tileset you view won't
have the 'signs' control

overviewer_core/data/js_src/views.js

@@ -216,6 +216,9 @@ overviewer.views.SignControlView = Backbone.View.extend({
     registerEvents: function(me) {
         google.maps.event.addListener(overviewer.map, 'maptypeid_changed', function(event) {
             overviewer.mapView.updateCurrentTileset();
+
+            // workaround IE issue.  bah!
+            if (typeof markers=="undefined") { return; }
             me.render();
             // hide markers, if necessary
             // for each markerSet, check: