check if windowStack is > 0 before doing anything

src/nimwin.nim

@@ -349,6 +349,7 @@ when isMainModule:
 
           let windowStack = filter(toSeq(getChildren(display)), (w) => not w.props.anyIt(it.name.in(ignored)))
 
+          if windowStack.len > 0:
             discard display.XSetInputFocus(windowStack[0].win, RevertToPointerRoot, CurrentTime)
             discard display.XRaiseWindow(windowStack[0].win)