souphttpsrc: don't fail when seeking past the end of the content

souphttpsrc: don't fail when seeking past the end of the content

Range errors are already turned into EOS when the size is not known.
Do the same thing if the request as outside the known content size.

This can be triggered by seeking in a queue2:
- Ensure that the range containing the end of the file is available.
- Seek into this range from a different range.
- queue2 creates a seek event with start=<file-size>
- this results in a "Requested Range Not Satisfiable" error

Fixes #452

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/merge_requests/385>