the IPC interface always reports the (last) focused window ID of the highest workspace

When switching between workspaces, `fht-compositor ipc focused-window` always reports the focused window ID of the highest workspace instead of the focused window ID of the current workspace. Example: if I create a window with ID 7 on workspace 5 and then move to workspace 4 and create (and focus) a window with ID 8, then `focused-window` reports window 7 (with "Current workspace ID: 5") even though I'm actually focussing window 8 and `focused-workspace` correctly reports 4. If I close all windows on the highest workspace, then the focused window on the next-highest workspace will be reported.