list of canvas types is cleared before refresh

frontend-js/src/main/js/gui/admin/EditProjectDialog.js

@@ -574,6 +574,7 @@ EditProjectDialog.prototype.refresh = function () {
     var configuration = self.getConfiguration();
     var mapCanvasTypes = configuration.getMapCanvasTypes();
     var select = $("[name='project-map-canvas-type']", self.getElement())[0];
+    $(select).empty();
     var licenceCheckbox = $("[name='project-google-maps-license']", self.getElement())[0];
     var licenceDiv = licenceCheckbox.parentElement.parentElement;