E.g. with the bugdoc from tdf#93553, most of the streams to save
are actually small, they just do not provide XSeekable. Since it
seems all the streams are already fully available by the time
the zip packaging is done, fallback to XInputStream::available()
to find out if the stream is small.
With this, the zipping part of saving tdf#93553 is now down
from ~1.5s to ~0.5s.
This presumably also makes the hack for tdf#93553 unnecessary.

Change-Id: Id9bb7d835400d6d8f147f5c11ade684a549aba53
Reviewed-on: https://gerrit.libreoffice.org/73030
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>