Only do tty validation when using a NCursesUI

src/main.cc

@@ -243,6 +243,8 @@ void create_local_client(StringView init_command)
         }
     };
 
+    if (std::is_same<UI, NCursesUI>::value)
+    {
         if (not isatty(1))
             throw runtime_error("stdout is not a tty");
 
@@ -255,6 +257,7 @@ void create_local_client(StringView init_command)
             close(tty);
             create_fifo_buffer("*stdin*", fd);
         }
+    }
 
     static Client* client = ClientManager::instance().create_client(
         make_unique<LocalUI>(), get_env_vars(), init_command);