Unary interceptors conflicts with gRPC-Web Developer Tools

I'v found that enabled gRPC-Web Developer Tools (by SafetyCulture) brokes up unary interceptors set up for grpc-web client. Interceptors are being not called when gRPC-Web Developer Tools are enabled.

Issue was found with next code:

```JS
const AuthInterceptor = function() {
this.intercept = function(request, invoker) {
request.getMetadata().Authorization = AuthService.GetAuthHeaderValue();

return invoker(request);
};
};

const options = {"unaryInterceptors": [new AuthInterceptor()]};
const APIClient = new APIPromiseClient(API_URL, null, options);

const enableDevTools = window.__GRPCWEB_DEVTOOLS__ || (() => {});
enableDevTools([
APIClient,
]);

APIClient.me(new ProtobufEmpty(), {})
.then(result => {
...
})
.catch(error => {
console.error(error); // <-- when gRPC-Web DevTools are enabled I receive error "no auth header" from my backend
});
```

Also, this bug was posted to gRPC-web Developers Tools repo: https://github.com/SafetyCulture/grpc-web-devtools/issues/80
and I think it it rather looks like their job to fix this issue on their side. But I want to warn people here about such compatibleness (so that they do not waste time guessing why their UnaryInterceptors not working).