patch 8.1.1615: crash when passing buffer number to popup_create()

Problem:    Crash when passing buffer number to popup_create(). (Yasuhiro
            Matsumoto)
Solution:   Initialze the window properly.
diff --git a/src/version.c b/src/version.c
index 8a9f347..ec541b4 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1615,
+/**/
     1614,
 /**/
     1613,