[Qt] 4-player / 4-score input doesn't work

[wangsitan]

Describe the bug
Player-3 and player-4 cannot input any keys (only happens in Qt version).

To Reproduce
Steps to reproduce the behavior:

1. Configure key mapping for player-3 and player-4.
2. Turn on the "attach 4-score" option.
3. Open a game that supports 4 players playing, such as Nekketsu Soccer League.
4. Input of player-3 and player-4 doesn't work.

Expected behavior
Input of player-3 and player-4 does work.

(please complete the following information):

• OS and Version: kubuntu 22.04, Windows 10
• Version of FCEUX used (QT or non-QT): Qt, both interim build and latest release.

Additional context
I also tried using fceux --input3 4player --input4 4player --fourscore 1, but it didn't work either.

The non-Qt version has a expansion called "4-Player Adapter", which is required for 4-player playing. But it is not listed on GUI of the Qt version.