patch 7.4.1592

Problem:    Quickfix code using memory after being freed. (Dominique Pelle)
Solution:   Detect that the window was closed. (Hirohito Higashi)

src/version.c

@@ -748,6 +748,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1592,
 /**/
     1591,
 /**/