Fixed a crash in error handing of rand_drbg_new

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Kurt Roeckx <kurt@roeckx.be>
Reviewed-by: Ben Kaduk <kaduk@mit.edu>
(Merged from https://github.com/openssl/openssl/pull/5646)

crypto/rand/drbg_lib.c

diff --git a/crypto/rand/drbg_lib.c b/crypto/rand/drbg_lib.c
index 360e775..02ad071 100644
--- a/crypto/rand/drbg_lib.c
+++ b/crypto/rand/drbg_lib.c
@@ -218,7 +218,7 @@
 
     if (drbg == NULL) {
         RANDerr(RAND_F_RAND_DRBG_NEW, ERR_R_MALLOC_FAILURE);
-        goto err;
+        return NULL;
     }
 
     drbg->secure = secure && CRYPTO_secure_allocated(drbg);