patch 8.2.1509: vertical separator is cleared when dragging a popup window

Problem:    Vertical separator is cleared when dragging a popup window using a
            multi-byte character for the border.
Solution:   Only clear the character before the window if it is using a
            multi-byte character. (closes #6766)

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1509,
 /**/
     1508,
 /**/