Add missing RAND initialisation call.

Reviewed-by: NBernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/7587)

crypto/rand/rand_lib.c

@@ -363,7 +363,8 @@ void rand_cleanup_int(void)
  */
 void RAND_keep_random_devices_open(int keep)
 {
-    rand_pool_keep_random_devices_open(keep);
+    if (RUN_ONCE(&rand_init, do_rand_init))
+        rand_pool_keep_random_devices_open(keep);
 }
 
 /*