Return HTTP 404 for non-existing admin pages

pkg/app/admin.go

@@ -50,6 +50,8 @@ func (h *adminHandler) Handle(user *auth.User, company *auth.Company, conn *data
 			default:
 				httplib.MethodNotAllowed(w, r, http.MethodGet)
 			}
+		default:
+			http.NotFound(w, r)
 		}
 	})
 }