compiling an empty function fails

[binji]

test from sexpr-wasm-prototype:

(module
  (export "f" $f)
  (func $f))

output:

+.../sexpr-wasm/test/wasm.js:8: WasmModule::Instantiate(): Compiling WASM function #0:f failed:Result = no trees created @+0
  +
  +var module = WASM.instantiateModule(buffer, ffi);
  +                  ^
  +

[titzer]

Fixed in 66bc3b5