typefind: doesn't set seqnum on new segment event, confusing oggdemux downstream
When operating in pull mode, typefind responds to seek events by generating a new segment event, but it fails to copy the seqnum across, which causes problems if something downstream is waiting until it sees a new segment event that matches the seek.
oggdemux operating in push mode, for example, issues seeks to get the file duration, then go back to the start of the file, and after each seek it drops any buffers it gets until it gets a matching new segment. When typefind handles this seek, it never gets a matching new segment event, so it drops buffers until eos.
An easy way to reproduce this is filesrc location=test.ogg ! typefind ! queue2 ! decodebin ! fakesink, roughly matching what uridecodebin does (which is how I ended up here, only streaming over sftp). Using pushfilesrc works correctly, as typefind doesn't end up in pull mode. Removing queue2 works, as then (I think) oggdemux can use pull mode. Removing typefind also works, as then something else handles the seek and does a better job of it.