Go Panic When Calling the `/runtime/init/error` Endpoint

```
time="2021-04-28T14:07:35.625" level=panic msg="ReplyStream not available"
2021/04/28 14:07:35 http: panic serving 127.0.0.1:52492: &{0xc000164000 map[] 2021-04-28 14:07:35.62583 +0000 UTC m=+2.137851001 panic ReplyStream not available }
goroutine 21 [running]:
net/http.(*conn).serve.func1(0xc000130aa0)
/usr/local/go/src/net/http/server.go:1800 +0x139
panic(0x866640, 0xc0001641c0)
/usr/local/go/src/runtime/panic.go:975 +0x3e3
github.com/sirupsen/logrus.Entry.log(0xc000164000, 0xc000106f00, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
/go/pkg/mod/github.com/sirupsen/logrus@v1.6.0/entry.go:259 +0x335
github.com/sirupsen/logrus.(*Entry).Log(0xc0001640e0, 0xc000000000, 0xc00008d588, 0x1, 0x1)
/go/pkg/mod/github.com/sirupsen/logrus@v1.6.0/entry.go:287 +0xeb
github.com/sirupsen/logrus.(*Logger).Log(0xc000164000, 0xc000000000, 0xc00008d588, 0x1, 0x1)
/go/pkg/mod/github.com/sirupsen/logrus@v1.6.0/logger.go:193 +0x7d
github.com/sirupsen/logrus.(*Logger).Panic(...)
/go/pkg/mod/github.com/sirupsen/logrus@v1.6.0/logger.go:234
github.com/sirupsen/logrus.Panic(...)
/go/pkg/mod/github.com/sirupsen/logrus@v1.6.0/exported.go:129
go.amzn.com/lambda/rapi/rendering.RenderInteropError(0x9097c0, 0xc00018c0e0, 0xc0001a8200, 0x902b60, 0xc0001050c0)
/LambdaRuntimeLocal/lambda/rapi/rendering/rendering.go:292 +0x9a
go.amzn.com/lambda/rapi/handler.(*initErrorHandler).ServeHTTP(0xc0002140a0, 0x9097c0, 0xc00018c0e0, 0xc0001a8200)
/LambdaRuntimeLocal/lambda/rapi/handler/initerror.go:52 +0x519
net/http.HandlerFunc.ServeHTTP(0xc000202380, 0x9097c0, 0xc00018c0e0, 0xc0001a8200)
/usr/local/go/src/net/http/server.go:2041 +0x44
github.com/go-chi/chi.(*Mux).routeHTTP(0xc00021e0c0, 0x9097c0, 0xc00018c0e0, 0xc0001a8200)
/go/pkg/mod/github.com/go-chi/chi@v4.1.2+incompatible/mux.go:431 +0x278
net/http.HandlerFunc.ServeHTTP(0xc000214030, 0x9097c0, 0xc00018c0e0, 0xc0001a8200)
/usr/local/go/src/net/http/server.go:2041 +0x44
go.amzn.com/lambda/rapi/middleware.RuntimeReleaseMiddleware.func1.1(0x9097c0, 0xc00018c0e0, 0xc0001a8200)
/LambdaRuntimeLocal/lambda/rapi/middleware/middleware.go:100 +0xea
net/http.HandlerFunc.ServeHTTP(0xc000202180, 0x9097c0, 0xc00018c0e0, 0xc0001a8200)
/usr/local/go/src/net/http/server.go:2041 +0x44
go.amzn.com/lambda/rapi/middleware.AccessLogMiddleware.func1.1(0x9097c0, 0xc00018c0e0, 0xc0001a8200)
/LambdaRuntimeLocal/lambda/rapi/middleware/middleware.go:77 +0x170
net/http.HandlerFunc.ServeHTTP(0xc0002021a0, 0x9097c0, 0xc00018c0e0, 0xc0001a8200)
/usr/local/go/src/net/http/server.go:2041 +0x44
go.amzn.com/lambda/rapi/middleware.AppCtxMiddleware.func1.1(0x9097c0, 0xc00018c0e0, 0xc0001a8100)
/LambdaRuntimeLocal/lambda/rapi/middleware/middleware.go:66 +0x77
net/http.HandlerFunc.ServeHTTP(0xc0002122d0, 0x9097c0, 0xc00018c0e0, 0xc0001a8100)
/usr/local/go/src/net/http/server.go:2041 +0x44
github.com/go-chi/chi.(*Mux).ServeHTTP(0xc00021e0c0, 0x9097c0, 0xc00018c0e0, 0xc0001a8100)
/go/pkg/mod/github.com/go-chi/chi@v4.1.2+incompatible/mux.go:70 +0x513
github.com/go-chi/chi.(*Mux).Mount.func1(0x9097c0, 0xc00018c0e0, 0xc0001a8100)
/go/pkg/mod/github.com/go-chi/chi@v4.1.2+incompatible/mux.go:298 +0x118
net/http.HandlerFunc.ServeHTTP(0xc0002023e0, 0x9097c0, 0xc00018c0e0, 0xc0001a8100)
/usr/local/go/src/net/http/server.go:2041 +0x44
github.com/go-chi/chi.(*Mux).routeHTTP(0xc00021e060, 0x9097c0, 0xc00018c0e0, 0xc0001a8100)
/go/pkg/mod/github.com/go-chi/chi@v4.1.2+incompatible/mux.go:431 +0x278
net/http.HandlerFunc.ServeHTTP(0xc0002140c0, 0x9097c0, 0xc00018c0e0, 0xc0001a8100)
/usr/local/go/src/net/http/server.go:2041 +0x44
github.com/go-chi/chi.(*Mux).ServeHTTP(0xc00021e060, 0x9097c0, 0xc00018c0e0, 0xc0001a8000)
/go/pkg/mod/github.com/go-chi/chi@v4.1.2+incompatible/mux.go:86 +0x2b2
net/http.serverHandler.ServeHTTP(0xc000222000, 0x9097c0, 0xc00018c0e0, 0xc0001a8000)
/usr/local/go/src/net/http/server.go:2836 +0xa3
net/http.(*conn).serve(0xc000130aa0, 0x90a800, 0xc00012e480)
/usr/local/go/src/net/http/server.go:1924 +0x86c
created by net/http.(*Server).Serve
/usr/local/go/src/net/http/server.go:2962 +0x35c
```

Here's a minimal example that reproduces this: https://github.com/chrisguitarguy/rie-init-error-example (`./run_example` there should do it).

Seems to originate from here: https://github.com/aws/aws-lambda-runtime-interface-emulator/blob/00d793b74124ebabf38da49fe3a34645e6168b5f/lambda/rapidcore/server.go#L223

There are some additional warnings that show up too:

```
time="2021-04-28T14:07:35.64" level=warning msg="Failed to send default error response: ErrInvalidInvokeID"
time="2021-04-28T14:07:35.64" level=error msg="INIT DONE failed: Runtime.ExitError"
time="2021-04-28T14:07:35.641" level=warning msg="Reset initiated: ReserveFail"
```

Looking at that `server.go`, it seems like it all depends on `invokeCtx` being set, but that wouldn't be set up for init errors given there is not invoke context yet -- something went wrong before it go to that point, right?

リンク先の最小限の例から ./run_example を使って失敗を再現し、その後、lambda/rapidcore/server.go の223行目付近、および lambda/rapi/rendering/rendering.go の292行目と lambda/rapi/handler/initerror.go の52行目を調査してください。init-error パスが invoke context を必要とせず、エンドポイントが Go panic や報告されたレスポンス警告なしに完了することを確認してください。

索引モデルが issue の本文から書いたものです。