bug#35927: 26.2; url-http-end-of-headers sets to 1 when cache is working

[Xu Chunyang]

Today I enable URL cache via

    (setq url-automatic-caching t
          url-cache-expire-time (* 6 3600))

and I notice url-http-end-of-headers isn't the end of the headers when
cache is working. This breaks some of my code, I assume it is the end of
the header so I use (goto-char url-http-end-of-headers) before parsing
the response body. Is this expected or a bug?

    (with-current-buffer (url-retrieve-synchronously "http://example.com";)
      (message "=> %S" url-http-end-of-headers))
    "=> #<marker at 347 in  *http example.com:80*>"
    
    (with-current-buffer (url-retrieve-synchronously "http://example.com";)
      (message "=> %S" url-http-end-of-headers))
    "=> #<marker at 1 in  *http example.com:80*-325608>"
    
    (with-current-buffer (url-retrieve-synchronously "http://example.com";)
      (message "=> %S" url-http-end-of-headers))
    "=> #<marker at 1 in  *http example.com:80*-887290>"