Fix HTTPClient keep alive with chunked encoding.

We need to consume the trailer part and final CRLF after last chunk
as per RFC 7230 section 4.1:

```
chunked-body   = *chunk
                 last-chunk
                 trailer-part
                 CRLF
```

We do not return the trailer part, just consume it allowing following
requests to work as expected when using keep alive.

core/io/http_client.h

@@ -172,6 +172,7 @@ private:
 	bool chunked;
 	Vector<uint8_t> chunk;
 	int chunk_left;
+	bool chunk_trailer_part;
 	int body_size;
 	int body_left;
 	bool read_until_eof;