patch 8.2.0142: possible to enter popup window with CTRL-W p

Problem:    Possible to enter popup window with CTRL-W p. (John Devin)
Solution:   Check entered window is not a popup window. (closes #5515)
diff --git a/src/popupwin.c b/src/popupwin.c
index e1f73bd..47e9238 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -2484,6 +2484,8 @@
     void
 close_all_popups(void)
 {
+    if (ERROR_IF_POPUP_WINDOW)
+	return;
     while (first_popupwin != NULL)
 	popup_close(first_popupwin->w_id);
     while (curtab->tp_first_popupwin != NULL)