window-picker: task items are not correctly freed if window has moved between monitors
It is possible that a task item is not correctly freed from its task list when a window is closed. This results in use after-free errors and incorrect behavior of the task items added to the applet.
This happens only in multi-monitor scenarios where at least two window-picker applets are present on different monitors. If the window is moved from one monitor to another monitor before the window is closed, then upon closing the window it can happen that the corresponding task item remains visible on the applet.