message: Crash early if wptr.deref(memory) returns None
diff: @@ -66,5 +66,6 @@ pub fn write_memory(ctx: &Ctx, ptr: u32, data: &[u8]) -> i32 {
  fn to_slice(ctx: &Ctx, ptr: u32) -> Slice {
  let memory = ctx.memory(0);
  let wptr = WasmPtr::<Slice>::new(ptr);
  - wptr.deref(memory).map(|x| x.get()).unwrap_or_default()
  + let cell = wptr.deref(memory).unwrap();
  + cell.get()
  }
  