The default BYTE DURATION basesrc query handler will return `-1` and TRUE. In
order to properly handle cases where upstream http servers didn't return a valid
Content-Length we also need to check whether it was valid when calculating
bitrates.
Avoids returning completely bogus bitrates with gogol's video streaming services
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1544>
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