x11-wm/kwinft: unbreak X-KDE-Wayland-Interfaces detection

$ pkg install kwinft vulkan-tools
$ export QT_LOGGING_RULES="kwin_*.debug=true"
$ kwin_wayland --exit-with-session vkcube-wayland
[...]
kwin_wl: Could not identify process with pid 12345

(cherry picked from commit 3ae6553cbd34c94c116757c0166876f63cfcde75)