souphttpsrc: Cookies property is ignored

Since #356 (closed) (soup session sharing, 1.14), the soup cookie jar feature has been enabled on the session. This soup session feature actually replaces/removes any existing Cookie header (https://gitlab.gnome.org/GNOME/libsoup/blob/64cd14cd0ef8d75bb8fbac5ece1fcd4903e455a4/libsoup/soup-cookie-jar.c#L812), so adding the header with the cookies from the property does nothing at the moment.

I have a patch for this which disables the cookie jar feature on the message if cookies are being set. Maybe src->cookies != NULL should be added to the can_share condition as well? I will create a PR after testing some more.