wcs: don't display "forms of a category" until it's configured (#7705)

combo/apps/wcs/models.py

@@ -260,6 +260,9 @@ class WcsFormsOfCategoryCell(WcsCommonCategoryCell, WcsBlurpMixin):
     def api_url(self):
         return self.category_reference.split(':')[1] + '/json'
 
+    def is_visible(self, user=None):
+        return self.category_reference
+
     def render(self, context):
         renderer = self.get_blurp_renderer(context)
         template = renderer.render_template()