patch 8.1.1649: Illegal memory access when closing popup window

Problem:    Illegal memory access when closing popup window.
Solution:   Get w_next before closing the window.
diff --git a/src/version.c b/src/version.c
index 4952b70..82f9093 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1649,
+/**/
     1648,
 /**/
     1647,