QHttpPart hangs reading from a QIODevice at pos() != 0

When trying to send a QFile via HTTP using QHttpPart, the upload fails if the QFile has been seek()'d beforehand.

It appears that QHttpPart uses QIODevice::size() to determine how much to read from the file, disregarding the current position of the QFile's read pointer, so if a seek() is executed, it will try to read more bytes than available, getting stuck in a loop.

A minimal example is attached. Run passing any file as the first argument. It will loop forever trying to read some bytes at the end of the file. Commenting f->seek(1); makes it work.