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>
diff --git a/src/version.c b/src/version.c
index 159fe3b..9cf6032 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    531,
+/**/
     530,
 /**/
     529,