Fix #2795: "check_availability" bug with saved searches.

app/controllers/concerns/saved_searches/check_availability.rb

@@ -0,0 +1,25 @@
+module SavedSearches
+  module CheckAvailability
+    extend ActiveSupport::Concern
+
+    included do
+      before_filter :check_availability
+    end
+
+    def check_availability
+      if !SavedSearch.enabled?
+        respond_to do |format|
+          format.html do
+            flash[:notice] = "Listbooru service is not configured. Saved searches are not available."
+            redirect_to :back
+          end
+          format.json do
+            render json: {success: false, reason: "Listbooru service is not configured"}.to_json, status: 501
+          end
+        end
+
+        return false
+      end
+    end
+  end
+end