Correctly handle trying to edit not existing settings tab (forem#1011)

app/controllers/users_controller.rb

@@ -173,6 +173,8 @@ def handle_settings_tab
         %0A
         YOUR-DEV-USERNAME-HERE
       HEREDOC
+    else
+      not_found unless @tab_list.map { |t| t.downcase.gsub(" ", "-") }.include? @tab
     end
   end
 end

spec/requests/user_settings_spec.rb

@@ -21,6 +21,11 @@
         end
       end
 
+      it "handles unknown settings tab properly" do
+        expect { get "/settings/does-not-exist" }.
+          to raise_error(ActionController::RoutingError)
+      end
+
       it "doesn't let user access membership if user has no monthly_dues" do
         get "/settings/membership"
         expect(response.body).not_to include("Settings for")