After network disconnection/connection, in progress HTTP requests retry with wrong range.

We are trying to download a remote file from a start offset to the end of file using this HTTP range request:

bytes=9500-

When we unplug the network cable, and then reconnect it after some seconds, another Get request is sent by Qt to resume download, However the new range request end offset is wrong, because Qt assumes that there is always an end offset for the HTTP range request. 

https://github.com/qt/qtbase/blob/53d62b8fcbb639bd625777c8f1c01764445fb1c4/src/network/access/qnetworkreplyhttpimpl.cpp#L753

so it sends this request that is wrong:

bytes=9500-0

We added the end offset to the request and the issue is fixed but in some situations we do not know the total downloading file size.
Also the RFC of ranged request states that the end offset is optional.