Only close ui panel if it is open

When calling ui.closePanel, this will fire "panel:closed", which
is listened by uMap to blindly call map.invalidateSize, which
creates trouble in the dashboard preview: when pressing twice ESC
key (eg. when switching from a preview to another), the map would pan once
to the north east (I guess because invalidateSize is called while
the map is not displayed, but not sure).

umap/static/umap/js/umap.ui.js

@@ -64,8 +64,10 @@ L.U.UI = L.Evented.extend({
   },
 
   closePanel: function () {
+    if (L.DomUtil.hasClass(this.parent, 'umap-ui')) {
       L.DomUtil.removeClass(this.parent, 'umap-ui')
       this.fire('panel:closed')
+    }
   },
 
   alert: function (e) {