wasm2js -O --emscripten crashes

```
wasm2js -O --emscripten work.wasm
```
crashes with an error message:
```
invalid type
UNREACHABLE executed at src/asmjs/asm_v_wasm.cpp:63!
Aborted
```

Found by the fuzzer. `work.wasm` was reduced by `wasm-reduce`. I attached `work.wasm` here.
[work.wasm.tar.gz](https://github.com/WebAssembly/binaryen/files/4001944/work.wasm.tar.gz)