Implements the same heuristic as Curl (and web browsers): if no `Content-Length`, no `Connection: keep-alive` and no chunked transfer encoding, assume th rest of the data until EOF is the body, gracefully setting the HTTP client back to the disconnected state.
Theoretically, this is not compliant with HTTP 1.1, by which `keep-alive` is the default, but in practice, an explicit header is sent by servers.
Using `misc/scripts/fix_headers.py` on all Godot files.
Some missing header guards were added, and the header inclusion order
was fixed in the Bullet module.
