patch 8.1.1433: win_execute() may leave popup window focused

Problem:    Win_execute() may leave popup window focused, eventually leading
            to a crash. (Bjorn Linse)
Solution:   When previous window was closed, go to the first window.
diff --git a/src/testdir/test_popupwin.vim b/src/testdir/test_popupwin.vim
index 29d4c15..d0d27b5 100644
--- a/src/testdir/test_popupwin.vim
+++ b/src/testdir/test_popupwin.vim
@@ -105,6 +105,14 @@
   call delete('XtestPopup')
 endfunc
 
+func Test_win_execute_closing_curwin()
+  split
+  let winid = popup_create('some text', {})
+  call win_execute(winid, winnr() .. "close")
+  call assert_equal(1, winnr())
+  popupclear
+endfunc
+
 func Test_popup_with_wrap()
   if !CanRunVimInTerminal()
     return