Unmarshaling empty string returns `io.EOF` error and it breaks/stops JSON unmarshaling

Maybe empty strings could be decoded into `NaN` or something better than an `io.EOF`? Just an idea.

Problem is when decoding JSON, which fails with an `io.EOF` error, which usually means that a `Reader` was already read. Funny to debug :)

Looks like the `io.EOF` comes from reading the sign at the start of `UnmarslaText(...)`.