souphttpsrc: do not emit error when connection with unknown size ends

souphttpsrc: do not emit error when connection with unknown size ends

Commit 46fd12ae5ec53200b16dfd7f17048d6bc60fbfbc introduced connection
recovery. But when server does not specify content-size,
souphttpsrc tries to reconnect even after regular end of stream.
Http server replies  with SOUP_STATUS_REQUESTED_RANGE_NOT_SATISFIABLE
but souphttpsrc still emits error instead of EOS.

https://bugzilla.gnome.org/show_bug.cgi?id=724717

Signed-off-by: Branislav Katreniak <bkatreniak@nuvotechnologies.com>