libvlc should report seekability when using imem
With imem a trial-and-error seekability is used (i.e. on seek requests the seek callback is called). Yet libvlc reports that the player is not seekable. So in a scenario where one would always ask the player whether it is seekable before trying to seek, one would never be able to seek with imem regardless of whether it could actually seek.
So either with imem as source libvlc should always report it as seekable or (better yet) introduce a callback to imem that asks whether it is seekable.