Fix double BIO_free in req

Reviewed-by: NTim Hudson <tjh@openssl.org>

apps/req.c

@@ -591,6 +591,7 @@ int req_main(int argc, char **argv)
             goto end;
         }
         BIO_free(out);
+        out = NULL;
         BIO_printf(bio_err, "-----\n");
     }