Document that SCT_set_source returns 0 on failure.

Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NMatt Caswell <matt@openssl.org>

doc/crypto/SCT_new.pod

@@ -170,7 +170,7 @@ B<SCT_set_signature_nid> returns 1 if the specified NID is supported, 0 otherwis
 B<SCT_set1_extensions> and B<SCT_set1_signature> return 1 if the supplied buffer
 is copied successfully, 0 otherwise (i.e. if malloc fails).
 
-B<SCT_set_source> will always return 1.
+B<SCT_set_source> returns 1 on success, 0 otherwise.
 
 =head1 SEE ALSO