`wast2json` miscompiles "if.wast" from the specification tests

The following WAST test expression from if.wast miscompiles, omitting the empty else block:

(assert_invalid
  (module (func $type-else-value-empty-vs-num (result i32)
    (if (result i32) (i32.const 1) (then (i32.const 0)) (else))
  ))
  "type mismatch"
)

$ wast2json if.wast
$ wasm-objdump -x -d if.0.wasm

if.0.wasm:	file format wasm 0x1

Section Details:

Type[1]:
 - type[0] () -> i32
Function[1]:
 - func[0] sig=0
Code[1]:
 - func[0] size=9

Code Disassembly:

000017 func[0]:
 000018: 41 01                      | i32.const 1
 00001a: 04 7f                      | if i32
 00001c: 41 00                      |   i32.const 0
 00001e: 0b                         | end
 00001f: 0b                         | end

WABT version: 0df6c26d2a6122afcc2c32ff6b608326258d40d9

Reproduce the issue with wast2json if.wast, then inspect the wast2json entry point and the handling of the WAST if expression containing an empty else block. Compare the generated if.0.wasm with the source expression and wasm-objdump output; done means the empty else block is preserved and the invalid type mismatch remains represented correctly.