Short code recovery is inflating precision

(From #273 )

Some implementations, notably Java, are inflating precision of padded short codes.

Mentioned by @bocops:
> @JonMcPherson mentioned that the Java implementation recovers short code "2300+" to "????23GG+". Inflating a code's precision like that seems like a bug to me.

Maybe add a note to the spec, but this should get a test case and update any implementations that fail.