TypeError logs from emrun

While debugging my Wasm module via DevTools, I noticed that the console output from `emrun` is periodically printing these error messages:

```
Exception occurred during processing of request from ('100.68.192.140', 49514)
Traceback (most recent call last):
File "/usr/lib/python3.9/socketserver.py", line 650, in process_request_thread
self.finish_request(request, client_address)
File "/usr/lib/python3.9/socketserver.py", line 360, in finish_request
self.RequestHandlerClass(request, client_address, self)
File "/usr/lib/python3.9/http/server.py", line 653, in __init__
super().__init__(*args, **kwargs)
File "/usr/lib/python3.9/socketserver.py", line 720, in __init__
self.handle()
File "/usr/lib/python3.9/http/server.py", line 427, in handle
self.handle_one_request()
File "/usr/lib/python3.9/http/server.py", line 415, in handle_one_request
method()
File "/ssd/smartcard/chromeos_smart_card_connector/env/emsdk/upstream/emscripten/emrun.py", line 714, in do_POST
data = self.rfile.read(int(self.headers['Content-Length']))
TypeError: int() argument must be a string, a bytes-like object or a number, not 'NoneType'
```

I'm not sure if this is really breaking anything.