check if a window is trackable before removing it

src/nimwin.nim

@@ -570,6 +570,7 @@ when isMainModule:
     elif (ev.theType == UnmapNotify):
       # Switch focus potentially when a window is unmapped
       windowZipper = windowZipper.zipperRemove(ev.xunmap.window)
+      if display.shouldTrackWindow(ev.xunmap.window.addr):
         let focus = windowZipper.zipperFocus
         if focus.isSome:
           discard display.XSetInputFocus(focus.get, RevertToPointerRoot, CurrentTime)