wasm-as should accept empty `then`

[zapashcanon]

Hi,

The following code is rejected by wasm-as:

(module
  (func $f (export "f") (param $n i32)
    (if (local.get $n) (then))
  )
)

$ wasm-as tmp.wast
[parse exception: expected more elements in list (at 3:23)]Fatal: error in parsing input

It's actually valid and accepted by the reference interpreter.

[tlively]

We're working on a new text parser that will handle this correctly.

[patrick96]

Looks like this has been resolved in 1d95fdc7805ef2f29b8b8b0cce8f7c8cc385edd0