Invalid value when resolving `int16` value from a struct

It is probably useless to submit bugs here, but.... there is a copy/paste typo in [this code](https://github.com/zsx/r3/blob/9c0f38a174ee62355ce5e4df1db86e56a1a7feec/src/core/t-struct.c#L78-L79)

It can be reproduced in code:
```rebol
>> s: make struct! [a: [int16] 333]
== make struct! [a: [int16] 77] ;<--- should be 333 instead of 77!
```