ext/taglib/gsttaglib.*: Fix newsegment event handling a bit. We need to cache the first newsegment event, because we ...

Original commit message from CVS:
* ext/taglib/gsttaglib.cc:
* ext/taglib/gsttaglib.h:
Fix newsegment event handling a bit. We need to
cache the first newsegment event, because we can't
adjust offsets yet when we get it, as we don't
know the size of the tag yet for sure at that point.
Also do some minor cleaning up here and there and add
some debug statements.