8741 wrong code for struct member inititalited using struct ctor

Generate an error if we need to decide if it is a ctor or a struct literal, when we haven't determined the size yet (so that we don't know if if it has a constructor). Since this whole thing is happening in a trySemantic block, it will try again later when it has found the ctor, and at that point, it will compile without error.

The wording for the error message is not very good, but I think this only happens while errors are gagged, so the message will never be visible.