patch 9.0.0824: crash when using win_move_separator() in other tab page

Problem:    Crash when using win_move_separator() in other tab page.
Solution:   Check for valid window in current tab page.
            (closes #11479, closes #11427)

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    824,
 /**/
     823,
 /**/