Check for NULL cleanup function before using it in encoder_process

encoder_process assumes a cleanup function has been set in the currently
in-use encoder during processing, which can lead to segfaults if said
function hasn't been set

Add a NULL check for this condition, returning -1 if it is not set

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/23069)

crypto/encode_decode/encoder_lib.c

@@ -59,6 +59,11 @@ int OSSL_ENCODER_to_bio(OSSL_ENCODER_CTX *ctx, BIO *out)
         return 0;
     }
 
+    if (ctx->cleanup == NULL || ctx->construct == NULL) {
+        ERR_raise(ERR_LIB_OSSL_ENCODER, ERR_R_INIT_FAIL);
+        return 0;
+    }
+
     return encoder_process(&data) > 0;
 }