emscripten_lazy_load_code causes errors on re-entry

([Small repro repo](https://gist.github.com/surma/01ccc19a26752b61b4d41fd137b15146))

I am playing around with `emscripten_lazy_load_code` and I am running into an error.

C++ code:

```c++
void my_other_printf(int param) { printf(">>>>>%d\n", param); }

void my_main(int param) {
if (param < 3) {
printf(">%d\n", param);
} else {
emscripten_lazy_load_code();
my_other_printf(param);
}
}
```

On my page, I am hooking up a button that calls `my_main` with increasing integers. So first click `param=1`, second click `param=2`, etc. Once `param >= 3`, it uses the other code branch that triggers the lazy-loading.

The third click triggers the lazy load and succeeds. The forth click triggers some questionable fetches and errors. The fifth and any subsequent clicks succeed as expected.