adaptivedemux: Handle more live seeking use-cases

adaptivedemux: Handle more live seeking use-cases

This commit fixes the following assumptions with live seeking:
1) start was always valid and of type GST_SEEK_TYPE_SET
2) direction was always forward
3) stop should be offsetted when handling non-accurate seeks before
   the range start position.

In order to handle more live seeking use-cases (including reverse playback),
only do non-accurate start/stop value clamping for GST_SEEK_TYPE_SET values.

Also add a bit more debugging lines for issues

https://bugzilla.gnome.org/show_bug.cgi?id=782330