Treat a whitespace-only header line as obs-fold

[kou]

The current implementation has a problem with the following case:

print("HTTP/1.1 200 OK\r\n")
print("Content-Length: 5\r\n")
print(" \t\r\n")
print("X-After: value\r\n")
print("\r\n")
print("hello")

The " \t\r\n" line should be processed as obs-fold in RFC 9112:

https://www.rfc-editor.org/rfc/rfc9112.html#section-5.2

obs-fold     = OWS CRLF RWS
             ; obsolete line folding

A user agent that receives an obs-fold in a response message that
is not within a "message/http" container MUST replace each received
obs-fold with one or more SP octets prior to interpreting the field
value.

But it's processed as the header part end:

Header:

HTTP/1.1 200 OK
Content-Length: 5

Body:

X-After: value

hello

It must be processed as the following (whitespace only obs-fold is ignored):

Header:

HTTP/1.1 200 OK
Content-Length: 5
X-After: value

Body:

hello