patch 9.1.0531: resource leak in mch_get_random()

Problem:  resource leak in mch_get_random() (after v9.1.0518)
Solution: close file descriptor after reading successfully
          from /dev/urandom

Signed-off-by: Christian Brabandt <cb@256bit.org>

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    531,
 /**/
     530,
 /**/