check *libctx which is allocated by OSSL_LIB_CTX_new()

Reviewed-by: NDmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: NMatt Caswell <matt@openssl.org>
Reviewed-by: NPaul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17740)

test/tls-provider.c

@@ -840,6 +840,9 @@ int tls_provider_init(const OSSL_CORE_HANDLE *handle,
 {
     OSSL_LIB_CTX *libctx = OSSL_LIB_CTX_new();
 
+    if (libctx == NULL)
+        return 0;
+
     *provctx = libctx;
 
     /*