async error

emcc: 3.1.0

async error

During the execution of an asynchronous function, if other tasks are inserted, the state of the Promise function will always be pending

【code】

```
#include
#include
#include
#include
#include

using namespace emscripten;

class Test {
public:
void printf() {
for (int i = 0; i < 1000; i++) {
std::cout<<"i: "<(u8"encode", val(text));
val digestValue = val::global()[u8"crypto"][u8"subtle"].call(u8"digest", val(u8"SHA-256"), data).await();
val base64 = val::global().call(u8"btoa", val::global()[u8"String"][u8"fromCharCode"].call(u8"apply", val::null(), val::global()[u8"Uint8Array"].new_(digestValue)));

return base64;
}
};

EMSCRIPTEN_BINDINGS(main) {

class_("Test")
.smart_ptr_constructor("Test", &std::make_shared)
.function("printf", &Test::printf)
.function(u8"GetBase64Sha256Normal", &Test::GetBase64Sha256Normal);
}
```

js:

```
console.log("before ");
const res = await Promise.all([test.getBase64Sha256Normal("helloworld"), test.printf()]);
console.log("after: ", res);
```

would not print the last : "after ………"