WebHost: Fix too-many-players error not showing (#4033)

* WebHost: fix 'too many players' error not showing

* WebHost, Tests: add basic tests for generate endpoint

* WebHost: hopefully make CodeQL happy with MAX_ROLL redirect

WebHostLib/generate.py

@@ -81,6 +81,7 @@ def start_generation(options: Dict[str, Union[dict, str]], meta: Dict[str, Any])
     elif len(gen_options) > app.config["MAX_ROLL"]:
         flash(f"Sorry, generating of multiworlds is limited to {app.config['MAX_ROLL']} players. "
               f"If you have a larger group, please generate it yourself and upload it.")
+        return redirect(url_for(request.endpoint, **(request.view_args or {})))
     elif len(gen_options) >= app.config["JOB_THRESHOLD"]:
         gen = Generation(
             options=pickle.dumps({name: vars(options) for name, options in gen_options.items()}),