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/os_unix.c b/src/os_unix.c
index b7da552..474d288 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -7740,7 +7740,10 @@
     if (fd == -1)
 	dev_urandom_state = FAIL;
     else if (read(fd, buf, len) == len)
+    {
 	dev_urandom_state = OK;
+	close(fd);
+    }
     else
     {
 	dev_urandom_state = FAIL;