test/helpers/handshake.c: Add check for OPENSSL_strdup

As the potential failure of the memory allocation, the OPENSSL_strdup()
could return NULL pointer and then be assigned to 'server_ctx'.
In order to tell the callers the failure of the configuration, it should
be better to return error.

Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17705)

test/helpers/handshake.c

diff --git a/test/helpers/handshake.c b/test/helpers/handshake.c
index 7171f90..cee11bb 100644
--- a/test/helpers/handshake.c
+++ b/test/helpers/handshake.c
@@ -633,6 +633,8 @@
     if (extra->server.session_ticket_app_data != NULL) {
         server_ctx_data->session_ticket_app_data =
             OPENSSL_strdup(extra->server.session_ticket_app_data);
+        if (!TEST_ptr(server_ctx_data->session_ticket_app_data))
+            goto err;
         SSL_CTX_set_session_ticket_cb(server_ctx, generate_session_ticket_cb,
                                       decrypt_session_ticket_cb, server_ctx_data);
     }
@@ -641,6 +643,8 @@
             goto err;
         server2_ctx_data->session_ticket_app_data =
             OPENSSL_strdup(extra->server2.session_ticket_app_data);
+        if (!TEST_ptr(server2_ctx_data->session_ticket_app_data))
+            goto err;
         SSL_CTX_set_session_ticket_cb(server2_ctx, NULL,
                                       decrypt_session_ticket_cb, server2_ctx_data);
     }